diff --git a/example/echo/echo_test.go b/example/echo/echo_test.go
index 0a6195a..4598ee8 100755
--- a/example/echo/echo_test.go
+++ b/example/echo/echo_test.go
@@ -204,7 +204,7 @@ func TestCallToEchoApp(t *testing.T) {
 				Port:   uint16(laddr.Port),
 			},
 		},
-		UserAgent: "gosip/1.o",
+		UserAgent: []byte("gosip/1.o"),
 		Payload:   sdp.New(rtpaddr, sdp.ULAWCodec, sdp.DTMFCodec),
 	}
 
diff --git a/example/options/options_test.go b/example/options/options_test.go
index 511d024..a4a5e9c 100755
--- a/example/options/options_test.go
+++ b/example/options/options_test.go
@@ -26,8 +26,8 @@ func TestOptions(t *testing.T) {
 		CallID:     util.GenerateCallID(),
 		Method:     "OPTIONS",
 		CSeqMethod: "OPTIONS",
-		Accept:     "application/sdp",
-		UserAgent:  "pokémon/1.o",
+		Accept:     []byte("application/sdp"),
+		UserAgent:  []byte("pokémon/1.o"),
 		Request: &sip.URI{
 			Scheme: "sip",
 			User:   "echo",
@@ -84,7 +84,7 @@ func TestOptions(t *testing.T) {
 	if !msg.IsResponse() || msg.Status != 200 || msg.Phrase != "OK" {
 		t.Error("Not OK :[")
 	}
-	if options.CallID != msg.CallID {
+	if !bytes.Equal(options.CallID, msg.CallID) {
 		t.Error("CallID didnt match")
 	}
 	if options.CSeq != msg.CSeq || options.CSeqMethod != msg.CSeqMethod {
diff --git a/example/rawsip/rawsip_test.go b/example/rawsip/rawsip_test.go
index be703c3..7537c49 100755
--- a/example/rawsip/rawsip_test.go
+++ b/example/rawsip/rawsip_test.go
@@ -41,7 +41,7 @@ func TestRawSIPOptions(t *testing.T) {
 		"Max-Forwards: 70\r\n" +
 		"To: <sip:" + raddr + ">\r\n" +
 		"From: <sip:" + laddr + ">;tag=" + fromtag + "\r\n" +
-		"Call-ID: " + callid + "\r\n" +
+		"Call-ID: " + string(callid) + "\r\n" +
 		"CSeq: " + strconv.Itoa(cseq) + " OPTIONS\r\n" +
 		"Contact: <sip:" + laddr + ">\r\n" +
 		"User-Agent: pokémon/1.o\r\n" +
diff --git a/sip/dialog.go b/sip/dialog.go
index b6007a3..0c306cf 100755
--- a/sip/dialog.go
+++ b/sip/dialog.go
@@ -248,7 +248,7 @@ func (dls *dialogState) handleMessage(msg *Msg) bool {
 		dls.errChan <- errors.New("Remote UA is using a strange SIP version")
 		return false
 	}
-	if msg.CallID != dls.request.CallID {
+	if !bytes.Equal(msg.CallID, dls.request.CallID) {
 		log.Printf("Received message doesn't match dialog")
 		return dls.send(NewResponse(msg, StatusCallTransactionDoesNotExist))
 	}
diff --git a/sip/messages.go b/sip/messages.go
index 5963d43..3f23907 100644
--- a/sip/messages.go
+++ b/sip/messages.go
@@ -20,7 +20,7 @@ func NewRequest(tp *Transport, method string, to, from *Addr) *Msg {
 		CallID:     util.GenerateCallID(),
 		CSeq:       util.GenerateCSeq(),
 		CSeqMethod: method,
-		UserAgent:  GosipUA,
+		UserAgent:  []byte(GosipUA),
 	}
 }
 
@@ -35,8 +35,8 @@ func NewResponse(msg *Msg, status int) *Msg {
 		CSeq:        msg.CSeq,
 		CSeqMethod:  msg.CSeqMethod,
 		RecordRoute: msg.RecordRoute,
-		UserAgent:   GosipUA,
-		Allow:       GosipAllow,
+		UserAgent:   []byte(GosipUA),
+		Allow:       []byte(GosipAllow),
 	}
 }
 
@@ -54,7 +54,7 @@ func NewAck(msg, invite *Msg) *Msg {
 		Route:              msg.RecordRoute.Reversed(),
 		Authorization:      invite.Authorization,
 		ProxyAuthorization: invite.ProxyAuthorization,
-		UserAgent:          GosipUA,
+		UserAgent:          []byte(GosipUA),
 	}
 }
 
diff --git a/sip/msg.go b/sip/msg.go
index 1144d3e..5a4fdcc 100755
--- a/sip/msg.go
+++ b/sip/msg.go
@@ -32,52 +32,56 @@ type Msg struct {
 	Route       *Addr  // Used for goose routing and loose routing
 	RecordRoute *Addr  // Used for loose routing
 	Contact     *Addr  // Where we send response packets or nil
-	CallID      string // Identifies call from invite to bye
+	CallID      []byte // Identifies call from INVITE to BYE; never empty, only absent
 	CSeq        int    // Counter for network packet ordering
 	CSeqMethod  string // Helps with matching to orig message
 	MaxForwards int    // 0 has context specific meaning
-	UserAgent   string
+	UserAgent   []byte // Name of the SIP stack
 
 	// All the other RFC 3261 headers in plus some extras.
-	Accept             string
-	AcceptContact      string
-	AcceptEncoding     string
-	AcceptLanguage     string
-	AlertInfo          string
-	Allow              string
-	AllowEvents        string
-	AuthenticationInfo string
-	Authorization      string
-	CallInfo           string
-	ContentDisposition string
-	ContentEncoding    string
-	ContentLanguage    string
-	Date               string
-	ErrorInfo          string
-	Event              string
+	//
+	// These byte slices will be nil if absent, in which case the header never
+	// appeared. If they are empty, then the header did appear, but without a
+	// value.
+	Accept             []byte
+	AcceptContact      []byte
+	AcceptEncoding     []byte
+	AcceptLanguage     []byte
+	AlertInfo          []byte
+	Allow              []byte
+	AllowEvents        []byte
+	AuthenticationInfo []byte
+	Authorization      []byte
+	CallInfo           []byte
+	ContentDisposition []byte
+	ContentEncoding    []byte
+	ContentLanguage    []byte
+	Date               []byte
+	ErrorInfo          []byte
+	Event              []byte
 	Expires            int // Seconds registration should expire.
-	InReplyTo          string
-	MIMEVersion        string
+	InReplyTo          []byte
+	MIMEVersion        []byte
 	MinExpires         int // Registrars need this when responding
-	Organization       string
+	Organization       []byte
 	PAssertedIdentity  *Addr // P-Asserted-Identity or nil (used for PSTN ANI)
-	Priority           string
-	ProxyAuthenticate  string
-	ProxyAuthorization string
-	ProxyRequire       string
-	ReferTo            string
-	ReferredBy         string
+	Priority           []byte
+	ProxyAuthenticate  []byte
+	ProxyAuthorization []byte
+	ProxyRequire       []byte
+	ReferTo            []byte
+	ReferredBy         []byte
 	RemotePartyID      *Addr // Evil twin of P-Asserted-Identity.
-	ReplyTo            string
-	Require            string
-	RetryAfter         string
-	Server             string
-	Subject            string
-	Supported          string
-	Timestamp          string
-	Unsupported        string
-	WWWAuthenticate    string
-	Warning            string
+	ReplyTo            []byte
+	Require            []byte
+	RetryAfter         []byte
+	Server             []byte
+	Subject            []byte
+	Supported          []byte
+	Timestamp          []byte
+	Unsupported        []byte
+	WWWAuthenticate    []byte
+	Warning            []byte
 
 	// Extension headers.
 	Headers Headers
@@ -139,14 +143,15 @@ func (msg *Msg) Append(b *bytes.Buffer) {
 		msg.appendVersion(b)
 		b.WriteString("\r\n")
 	} else {
-		if msg.Phrase == "" {
-			msg.Phrase = Phrase(msg.Status)
-		}
 		msg.appendVersion(b)
 		b.WriteString(" ")
 		b.WriteString(strconv.Itoa(msg.Status))
 		b.WriteString(" ")
-		b.WriteString(msg.Phrase)
+		if msg.Phrase == "" {
+			b.WriteString(Phrase(msg.Status))
+		} else {
+			b.WriteString(msg.Phrase)
+		}
 		b.WriteString("\r\n")
 	}
 
@@ -183,7 +188,7 @@ func (msg *Msg) Append(b *bytes.Buffer) {
 	}
 
 	b.WriteString("Call-ID: ")
-	b.WriteString(msg.CallID)
+	b.Write(msg.CallID)
 	b.WriteString("\r\n")
 
 	b.WriteString("CSeq: ")
@@ -192,9 +197,9 @@ func (msg *Msg) Append(b *bytes.Buffer) {
 	b.WriteString(msg.CSeqMethod)
 	b.WriteString("\r\n")
 
-	if msg.UserAgent != "" {
+	if msg.UserAgent != nil {
 		b.WriteString("User-Agent: ")
-		b.WriteString(msg.UserAgent)
+		b.Write(msg.UserAgent)
 		b.WriteString("\r\n")
 	}
 
@@ -208,93 +213,93 @@ func (msg *Msg) Append(b *bytes.Buffer) {
 		}
 	}
 
-	if msg.Accept != "" {
+	if msg.Accept != nil {
 		b.WriteString("Accept: ")
-		b.WriteString(msg.Accept)
+		b.Write(msg.Accept)
 		b.WriteString("\r\n")
 	}
 
-	if msg.AcceptEncoding != "" {
+	if msg.AcceptEncoding != nil {
 		b.WriteString("Accept-Encoding: ")
-		b.WriteString(msg.AcceptEncoding)
+		b.Write(msg.AcceptEncoding)
 		b.WriteString("\r\n")
 	}
 
-	if msg.AcceptLanguage != "" {
+	if msg.AcceptLanguage != nil {
 		b.WriteString("Accept-Language: ")
-		b.WriteString(msg.AcceptLanguage)
+		b.Write(msg.AcceptLanguage)
 		b.WriteString("\r\n")
 	}
 
-	if msg.AlertInfo != "" {
+	if msg.AlertInfo != nil {
 		b.WriteString("Alert-Info: ")
-		b.WriteString(msg.AlertInfo)
+		b.Write(msg.AlertInfo)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Allow != "" {
+	if msg.Allow != nil {
 		b.WriteString("Allow: ")
-		b.WriteString(msg.Allow)
+		b.Write(msg.Allow)
 		b.WriteString("\r\n")
 	}
 
-	if msg.AllowEvents != "" {
+	if msg.AllowEvents != nil {
 		b.WriteString("Allow-Events: ")
-		b.WriteString(msg.AllowEvents)
+		b.Write(msg.AllowEvents)
 		b.WriteString("\r\n")
 	}
 
-	if msg.AuthenticationInfo != "" {
+	if msg.AuthenticationInfo != nil {
 		b.WriteString("Authentication-Info: ")
-		b.WriteString(msg.AuthenticationInfo)
+		b.Write(msg.AuthenticationInfo)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Authorization != "" {
+	if msg.Authorization != nil {
 		b.WriteString("Authorization: ")
-		b.WriteString(msg.Authorization)
+		b.Write(msg.Authorization)
 		b.WriteString("\r\n")
 	}
 
-	if msg.CallInfo != "" {
+	if msg.CallInfo != nil {
 		b.WriteString("Call-Info: ")
-		b.WriteString(msg.CallInfo)
+		b.Write(msg.CallInfo)
 		b.WriteString("\r\n")
 	}
 
-	if msg.ContentDisposition != "" {
+	if msg.ContentDisposition != nil {
 		b.WriteString("Content-Disposition: ")
-		b.WriteString(msg.ContentDisposition)
+		b.Write(msg.ContentDisposition)
 		b.WriteString("\r\n")
 	}
 
-	if msg.ContentEncoding != "" {
+	if msg.ContentEncoding != nil {
 		b.WriteString("Content-Encoding: ")
-		b.WriteString(msg.ContentEncoding)
+		b.Write(msg.ContentEncoding)
 		b.WriteString("\r\n")
 	}
 
-	if msg.ContentLanguage != "" {
+	if msg.ContentLanguage != nil {
 		b.WriteString("Content-Language: ")
-		b.WriteString(msg.ContentLanguage)
+		b.Write(msg.ContentLanguage)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Date != "" {
+	if msg.Date != nil {
 		b.WriteString("Date: ")
-		b.WriteString(msg.Date)
+		b.Write(msg.Date)
 		b.WriteString("\r\n")
 	}
 
-	if msg.ErrorInfo != "" {
+	if msg.ErrorInfo != nil {
 		b.WriteString("Error-Info: ")
-		b.WriteString(msg.ErrorInfo)
+		b.Write(msg.ErrorInfo)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Event != "" {
+	if msg.Event != nil {
 		b.WriteString("Event: ")
-		b.WriteString(msg.Event)
+		b.Write(msg.Event)
 		b.WriteString("\r\n")
 	}
 
@@ -305,15 +310,15 @@ func (msg *Msg) Append(b *bytes.Buffer) {
 		b.WriteString("\r\n")
 	}
 
-	if msg.InReplyTo != "" {
+	if msg.InReplyTo != nil {
 		b.WriteString("In-Reply-To: ")
-		b.WriteString(msg.InReplyTo)
+		b.Write(msg.InReplyTo)
 		b.WriteString("\r\n")
 	}
 
-	if msg.MIMEVersion != "" {
+	if msg.MIMEVersion != nil {
 		b.WriteString("MIME-Version: ")
-		b.WriteString(msg.MIMEVersion)
+		b.Write(msg.MIMEVersion)
 		b.WriteString("\r\n")
 	}
 
@@ -323,9 +328,9 @@ func (msg *Msg) Append(b *bytes.Buffer) {
 		b.WriteString("\r\n")
 	}
 
-	if msg.Organization != "" {
+	if msg.Organization != nil {
 		b.WriteString("Organization: ")
-		b.WriteString(msg.Organization)
+		b.Write(msg.Organization)
 		b.WriteString("\r\n")
 	}
 
@@ -335,39 +340,39 @@ func (msg *Msg) Append(b *bytes.Buffer) {
 		b.WriteString("\r\n")
 	}
 
-	if msg.Priority != "" {
+	if msg.Priority != nil {
 		b.WriteString("Priority: ")
-		b.WriteString(msg.Priority)
+		b.Write(msg.Priority)
 		b.WriteString("\r\n")
 	}
 
-	if msg.ProxyAuthenticate != "" {
+	if msg.ProxyAuthenticate != nil {
 		b.WriteString("Proxy-Authenticate: ")
-		b.WriteString(msg.ProxyAuthenticate)
+		b.Write(msg.ProxyAuthenticate)
 		b.WriteString("\r\n")
 	}
 
-	if msg.ProxyAuthorization != "" {
+	if msg.ProxyAuthorization != nil {
 		b.WriteString("Proxy-Authorization: ")
-		b.WriteString(msg.ProxyAuthorization)
+		b.Write(msg.ProxyAuthorization)
 		b.WriteString("\r\n")
 	}
 
-	if msg.ProxyRequire != "" {
+	if msg.ProxyRequire != nil {
 		b.WriteString("Proxy-Require: ")
-		b.WriteString(msg.ProxyRequire)
+		b.Write(msg.ProxyRequire)
 		b.WriteString("\r\n")
 	}
 
-	if msg.ReferTo != "" {
+	if msg.ReferTo != nil {
 		b.WriteString("Refer-To: ")
-		b.WriteString(msg.ReferTo)
+		b.Write(msg.ReferTo)
 		b.WriteString("\r\n")
 	}
 
-	if msg.ReferredBy != "" {
+	if msg.ReferredBy != nil {
 		b.WriteString("Referred-By: ")
-		b.WriteString(msg.ReferredBy)
+		b.Write(msg.ReferredBy)
 		b.WriteString("\r\n")
 	}
 
@@ -377,63 +382,63 @@ func (msg *Msg) Append(b *bytes.Buffer) {
 		b.WriteString("\r\n")
 	}
 
-	if msg.ReplyTo != "" {
+	if msg.ReplyTo != nil {
 		b.WriteString("Reply-To: ")
-		b.WriteString(msg.ReplyTo)
+		b.Write(msg.ReplyTo)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Require != "" {
+	if msg.Require != nil {
 		b.WriteString("Require: ")
-		b.WriteString(msg.Require)
+		b.Write(msg.Require)
 		b.WriteString("\r\n")
 	}
 
-	if msg.RetryAfter != "" {
+	if msg.RetryAfter != nil {
 		b.WriteString("RetryAfter: ")
-		b.WriteString(msg.RetryAfter)
+		b.Write(msg.RetryAfter)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Server != "" {
+	if msg.Server != nil {
 		b.WriteString("Server: ")
-		b.WriteString(msg.Server)
+		b.Write(msg.Server)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Subject != "" {
+	if msg.Subject != nil {
 		b.WriteString("Subject: ")
-		b.WriteString(msg.Subject)
+		b.Write(msg.Subject)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Supported != "" {
+	if msg.Supported != nil {
 		b.WriteString("Supported: ")
-		b.WriteString(msg.Supported)
+		b.Write(msg.Supported)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Timestamp != "" {
+	if msg.Timestamp != nil {
 		b.WriteString("Timestamp: ")
-		b.WriteString(msg.Timestamp)
+		b.Write(msg.Timestamp)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Unsupported != "" {
+	if msg.Unsupported != nil {
 		b.WriteString("Unsupported: ")
-		b.WriteString(msg.Unsupported)
+		b.Write(msg.Unsupported)
 		b.WriteString("\r\n")
 	}
 
-	if msg.Warning != "" {
+	if msg.Warning != nil {
 		b.WriteString("Warning: ")
-		b.WriteString(msg.Warning)
+		b.Write(msg.Warning)
 		b.WriteString("\r\n")
 	}
 
-	if msg.WWWAuthenticate != "" {
+	if msg.WWWAuthenticate != nil {
 		b.WriteString("WWW-Authenticate: ")
-		b.WriteString(msg.WWWAuthenticate)
+		b.Write(msg.WWWAuthenticate)
 		b.WriteString("\r\n")
 	}
 
diff --git a/sip/msg_parse.go b/sip/msg_parse.go
index ca785b8..d2a3f5f 100644
--- a/sip/msg_parse.go
+++ b/sip/msg_parse.go
@@ -61,7 +61,7 @@ func ParseMsgBytes(data []byte) (msg *Msg, err error) {
 	ctype := ""
 	var name string
 	var hex byte
-	var value *string
+	var value *[]byte
 	var via *Via
 	var addrp **Addr
 	var addr *Addr
@@ -9591,7 +9591,7 @@ tr403:
 {
 	b := data[mark:p - 1]
 	if value != nil {
-		*value = string(b)
+		*value = b
 	} else {
 		if msg.Headers == nil {
 			msg.Headers = Headers{}
@@ -11779,7 +11779,7 @@ tr553:
 tr557:
 //line sip.rl:205
 
-	msg.CallID = string(data[mark:p])
+	msg.CallID = data[mark:p]
 
 	goto st381
 tr643:
diff --git a/sip/msg_parse.rl b/sip/msg_parse.rl
index 623a441..4672893 100644
--- a/sip/msg_parse.rl
+++ b/sip/msg_parse.rl
@@ -38,7 +38,7 @@ func ParseMsgBytes(data []byte) (msg *Msg, err error) {
 	ctype := ""
 	var name string
 	var hex byte
-	var value *string
+	var value *[]byte
 	var via *Via
 	var addrp **Addr
 	var addr *Addr
diff --git a/sip/msg_test.go b/sip/msg_test.go
index b263689..db189ea 100755
--- a/sip/msg_test.go
+++ b/sip/msg_test.go
@@ -92,12 +92,12 @@ var msgTests = []msgTest{
 			VersionMajor: 2,
 			Status:       200,
 			Phrase:       "OK",
-			Warning: "Morning and evening\r\n" +
+			Warning: []byte("Morning and evening\r\n" +
 				" Maids heard the goblins cry:\r\n" +
 				" “Come buy our orchard fruits,\r\n" +
 				" Come buy, come buy:\r\n" +
 				" Apples and quinces,\r\n" +
-				" Lemons and oranges",
+				" Lemons and oranges"),
 		},
 	},
 
@@ -116,12 +116,12 @@ var msgTests = []msgTest{
 			VersionMajor: 2,
 			Status:       200,
 			Phrase:       "OK",
-			Warning: "Morning and evening\r\n" +
+			Warning: []byte("Morning and evening\r\n" +
 				" Maids heard the goblins cry:\r\n" +
 				" “Come buy our orchard fruits,\r\n" +
 				" Come buy, come buy:\r\n" +
 				" Apples and quinces,\r\n" +
-				" Lemons and oranges",
+				" Lemons and oranges"),
 			Headers: sip.Headers{
 				"X-LOL": "omfg",
 			},
@@ -459,7 +459,7 @@ var msgTests = []msgTest{
 			VersionMajor: 2,
 			Status:       200,
 			Phrase:       "OK",
-			Warning:      "Maids heard the goblins cry",
+			Warning:      []byte("Maids heard the goblins cry"),
 			Via: &sip.Via{
 				Protocol:  "SIP",
 				Version:   "2.0",
@@ -635,7 +635,7 @@ var msgTests = []msgTest{
 			Method:       "OPTIONS",
 			CSeqMethod:   "OPTIONS",
 			MaxForwards:  60,
-			CallID:       "e71a163e-c440-474d-a4ec-5cd85a0309c6",
+			CallID:       []byte("e71a163e-c440-474d-a4ec-5cd85a0309c6"),
 			CSeq:         36612,
 			Request: &sip.URI{
 				Scheme: "sip",
@@ -673,8 +673,8 @@ var msgTests = []msgTest{
 					Port:   42367,
 				},
 			},
-			UserAgent: "ghoul/0.1",
-			Accept:    "application/sdp",
+			UserAgent: []byte("ghoul/0.1"),
+			Accept:    []byte("application/sdp"),
 		},
 	},
 
@@ -708,12 +708,12 @@ var msgTests = []msgTest{
 			VersionMajor: 2,
 			Status:       200,
 			Phrase:       "OK",
-			CallID:       "99042736-d40b-4d96-a81b-867321443ff5",
+			CallID:       []byte("99042736-d40b-4d96-a81b-867321443ff5"),
 			CSeq:         16378,
 			CSeqMethod:   "INVITE",
-			Server:       "Asterisk PBX 10.11.1",
-			Allow:        "INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH",
-			Supported:    "replaces, timer",
+			Server:       []byte("Asterisk PBX 10.11.1"),
+			Allow:        []byte("INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH"),
+			Supported:    []byte("replaces, timer"),
 			Via: &sip.Via{
 				Protocol:  "SIP",
 				Version:   "2.0",
@@ -804,7 +804,7 @@ var msgTests = []msgTest{
 			VersionMajor: 2,
 			Status:       200,
 			Phrase:       "OK",
-			CallID:       "042736d4-0bd9-4681-ab86-7321443ff58a",
+			CallID:       []byte("042736d4-0bd9-4681-ab86-7321443ff58a"),
 			CSeq:         31109,
 			CSeqMethod:   "INVITE",
 			Via: &sip.Via{
@@ -905,7 +905,7 @@ var msgTests = []msgTest{
 			Method:       "INVITE",
 			CSeqMethod:   "INVITE",
 			MaxForwards:  70,
-			CallID:       "87704115-03b8-122e-08b5-001bfcce6bdf",
+			CallID:       []byte("87704115-03b8-122e-08b5-001bfcce6bdf"),
 			CSeq:         133097268,
 			Request: &sip.URI{
 				Scheme: "sip",
@@ -947,11 +947,11 @@ var msgTests = []msgTest{
 				// 	},
 				// },
 			},
-			UserAgent:          "tube/0.1",
-			Allow:              "INVITE, ACK, BYE, CANCEL, OPTIONS, PRACK, MESSAGE, SUBSCRIBE, NOTIFY, REFER, UPDATE, INFO",
-			AllowEvents:        "talk",
-			ContentDisposition: "session",
-			Supported:          "timer, 100rel",
+			UserAgent:          []byte("tube/0.1"),
+			Allow:              []byte("INVITE, ACK, BYE, CANCEL, OPTIONS, PRACK, MESSAGE, SUBSCRIBE, NOTIFY, REFER, UPDATE, INFO"),
+			AllowEvents:        []byte("talk"),
+			ContentDisposition: []byte("session"),
+			Supported:          []byte("timer, 100rel"),
 			Payload: &sip.MiscPayload{
 				T: "application/sdp-lol",
 				D: []byte("v=0\r\n" +
@@ -1034,9 +1034,10 @@ var msgTests = []msgTest{
 				Param: &sip.Param{"tag", "98asjd8", nil},
 			},
 			MaxForwards: 68,
-			CallID:      "wsinv.ndaksdj@192.0.2.1",
+			CallID:      []byte("wsinv.ndaksdj@192.0.2.1"),
 			CSeq:        9,
 			CSeqMethod:  "INVITE",
+			Subject:     []byte{},
 			Via: &sip.Via{
 				Protocol:  "SIP",
 				Version:   "2.0",
@@ -1058,7 +1059,6 @@ var msgTests = []msgTest{
 					},
 				},
 			},
-			Subject: "",
 			Headers: sip.Headers{
 				"NewFangledHeader": "newfangled value\r\n" +
 					" continued newfangled value",
@@ -1131,7 +1131,7 @@ var msgTests = []msgTest{
 		msg: sip.Msg{
 			VersionMajor: 2,
 			Method:       "!interesting-Method0123456789_*+`.%indeed'~",
-			CallID:       "intmeth.word%ZK-!.*_+'@word`~)(><:\\/\"][?}{",
+			CallID:       []byte("intmeth.word%ZK-!.*_+'@word`~)(><:\\/\"][?}{"),
 			CSeq:         139122385,
 			CSeqMethod:   "!interesting-Method0123456789_*+`.%indeed'~",
 			MaxForwards:  255,
diff --git a/sip/route.go b/sip/route.go
index 84df40e..1ba34db 100644
--- a/sip/route.go
+++ b/sip/route.go
@@ -27,7 +27,7 @@ func PopulateMessage(via *Via, contact *Addr, msg *Msg) {
 			msg.From = msg.Contact.Copy()
 			msg.From.Uri.Param = nil
 		}
-		if msg.CallID == "" {
+		if msg.CallID == nil {
 			msg.CallID = util.GenerateCallID()
 		}
 		if msg.CSeq == 0 {
@@ -39,8 +39,8 @@ func PopulateMessage(via *Via, contact *Addr, msg *Msg) {
 		if msg.MaxForwards == 0 {
 			msg.MaxForwards = 70
 		}
-		if msg.UserAgent == "" {
-			msg.UserAgent = GosipUA
+		if msg.UserAgent == nil {
+			msg.UserAgent = []byte(GosipUA)
 		}
 		if msg.Via.Param.Get("branch") == nil {
 			msg.Via.Param = &Param{"branch", util.GenerateBranch(), msg.Via.Param}
diff --git a/sip/sip.rl b/sip/sip.rl
index 365d19f..ee98cea 100644
--- a/sip/sip.rl
+++ b/sip/sip.rl
@@ -162,7 +162,7 @@ action name {
 action value {{
 	b := data[mark:p - 1]
 	if value != nil {
-		*value = string(b)
+		*value = b
 	} else {
 		if msg.Headers == nil {
 			msg.Headers = Headers{}
@@ -203,7 +203,7 @@ action Addr {
 }
 
 action CallID {
-	msg.CallID = string(data[mark:p])
+	msg.CallID = data[mark:p]
 }
 
 action ContentLength {
diff --git a/util/util.go b/util/util.go
index e6ce0ac..def66b2 100755
--- a/util/util.go
+++ b/util/util.go
@@ -1,6 +1,7 @@
 package util
 
 import (
+	"bytes"
 	"encoding/hex"
 	"math/rand"
 	"net"
@@ -70,13 +71,21 @@ func GenerateBranch() string {
 	return "z9hG4bK-" + GenerateTag()
 }
 
-// Generates a secure UUID4, e.g.f47ac10b-58cc-4372-a567-0e02b2c3d479
-func GenerateCallID() string {
+// Generates a secure UUID4, e.g. f47ac10b-58cc-4372-a567-0e02b2c3d479
+func GenerateCallID() []byte {
 	lol := randomBytes(15)
 	digs := hex.EncodeToString(lol)
-	uuid4 := digs[0:8] + "-" + digs[8:12] + "-4" + digs[12:15] +
-		"-a" + digs[15:18] + "-" + digs[18:]
-	return uuid4
+	var b bytes.Buffer
+	b.WriteString(digs[0:8])
+	b.WriteByte('-')
+	b.WriteString(digs[8:12])
+	b.WriteString("-4")
+	b.WriteString(digs[12:15])
+	b.WriteString("-a")
+	b.WriteString(digs[15:18])
+	b.WriteByte('-')
+	b.WriteString(digs[18:])
+	return b.Bytes()
 }
 
 // Generates a random ID for an SDP.