diff --git a/src/Dialogs.js b/src/Dialogs.js
index 69fe3cd17..b97485d79 100644
--- a/src/Dialogs.js
+++ b/src/Dialogs.js
@@ -139,7 +139,7 @@ JsSIP.Dialog.prototype = {
     } else if(request.method !== JsSIP.c.INVITE && request.cseq < this.remote_seqnum) {
         //Do not try to reply to an ACK request.
         if (request.method !== JsSIP.c.ACK) {
-          request.reply(500, JsSIP.c.REASON_500);
+          request.reply(500);
         }
         return false;
     } else if(request.cseq > this.remote_seqnum) {
@@ -152,17 +152,17 @@ JsSIP.Dialog.prototype = {
         if(request.cseq < this.remote_seqnum) {
           if(this.state === JsSIP.c.DIALOG_EARLY) {
             var retryAfter = (Math.random() * 10 | 0) + 1;
-            request.reply(500, JsSIP.c.REASON_500, [
+            request.reply(500, JsSIP.c.REASON_PHRASE[500], [
               'Retry-After:'+ retryAfter
             ]);
           } else {
-            request.reply(500, JsSIP.c.REASON_500);
+            request.reply(500);
           }
           return false;
         }
         // RFC3261 14.2
         if(this.state === JsSIP.c.DIALOG_EARLY) {
-          request.reply(491, JsSIP.c.REASON_491);
+          request.reply(491);
           return false;
         }
         // RFC3261 12.2.2 Replace the dialog`s remote target URI
diff --git a/src/Message.js b/src/Message.js
index 12687ec25..e5160c692 100644
--- a/src/Message.js
+++ b/src/Message.js
@@ -167,14 +167,14 @@ JsSIP.Message.prototype.init_incoming = function(request) {
   this.remote_identity = request.s('from').uri;
 
   this.accept = function() {
-    request.reply(200, JsSIP.c.REASON_200);
+    request.reply(200);
   };
 
   this.reject = function(status_code, reason_phrase) {
     if (status_code && reason_phrase) {
       request.reply(status_code, reason_phrase);
     } else {
-      request.reply(480, JsSIP.c.REASON_480);
+      request.reply(480);
     }
   };
 
@@ -188,9 +188,9 @@ JsSIP.Message.prototype.init_incoming = function(request) {
     transaction = this.ua.transactions.nist[request.via_branch];
 
     if (transaction && (transaction.state === JsSIP.c.TRANSACTION_TRYING || transaction.state === JsSIP.c.TRANSACTION_PROCEEDING)) {
-      request.reply(200, JsSIP.c.REASON_200);
+      request.reply(200);
     }
   } else {
-    request.reply(415, JsSIP.c.REASON_415, ["Accept: text/plain, text/html"]);
+    request.reply(415, JsSIP.c.REASON_PHRASE[415], ["Accept: text/plain, text/html"]);
   }
 };
diff --git a/src/SIPMessage.js b/src/SIPMessage.js
index a93c68cb9..c67b5cc1f 100644
--- a/src/SIPMessage.js
+++ b/src/SIPMessage.js
@@ -343,14 +343,16 @@ JsSIP.IncomingRequest.prototype = new JsSIP.IncomingMessage();
 * @param {Function} [onFailure] onFailure callback
 */
 JsSIP.IncomingRequest.prototype.reply = function(code, reason, extraHeaders, body, onSuccess, onFailure) {
-  var rr, vias, header, length, idx,
-    response = 'SIP/2.0 ' + code + ' ' + reason + '\r\n',
+  var rr, vias, header, length, idx, response,
     to = this.getHeader('To'),
     r = 0,
     v = 0;
 
+  reason = reason || JsSIP.c.REASON_PHRASE[code] || ' ';
   extraHeaders = extraHeaders || [];
 
+  response = 'SIP/2.0 ' + code + ' ' + reason + '\r\n';
+
   if(this.method === JsSIP.c.INVITE && code > 100 && code <= 200) {
     rr = this.countHeader('record-route');
 
@@ -401,10 +403,13 @@ JsSIP.IncomingRequest.prototype.reply = function(code, reason, extraHeaders, bod
 * @param {String} reason reason phrase
 */
 JsSIP.IncomingRequest.prototype.reply_sl = function(code, reason) {
-  var to,
-    response = 'SIP/2.0 ' + code + ' ' + reason + '\r\n',
+  var to, response,
     vias = this.countHeader('via');
 
+  reason = reason || JsSIP.c.REASON_PHRASE[code] || ' ';
+
+  response = 'SIP/2.0 ' + code + ' ' + reason + '\r\n';
+
   for(var v = 0; v < vias; v++) {
     response += 'Via: ' + this.getHeader('via', v) + '\r\n';
   }
diff --git a/src/SanityCheck.js b/src/SanityCheck.js
index ad0227237..939562afa 100644
--- a/src/SanityCheck.js
+++ b/src/SanityCheck.js
@@ -37,7 +37,7 @@ JsSIP.sanityCheck = (function() {
   // Sanity Check functions for requests
   function rfc3261_8_2_2_1() {
     if(message.s('to').scheme !== 'sip') {
-      reply(416, JsSIP.c.REASON_416);
+      reply(416);
       return false;
     }
   }
@@ -45,7 +45,7 @@ JsSIP.sanityCheck = (function() {
   function rfc3261_16_3_4() {
     if(!message.to_tag) {
       if(message.call_id.substr(0, 5) === ua.configuration.jssip_id) {
-        reply(482, JsSIP.c.REASON_482);
+        reply(482);
         return false;
       }
     }
@@ -56,7 +56,7 @@ JsSIP.sanityCheck = (function() {
     contentLength = message.getHeader('content-length');
 
     if(len < contentLength) {
-      reply(400, JsSIP.c.REASON_400);
+      reply(400);
       return false;
     }
   }
@@ -76,7 +76,7 @@ JsSIP.sanityCheck = (function() {
           for(idx in ua.transactions.ist) {
             tr = ua.transactions.ist[idx];
             if(tr.request.from_tag === fromTag && tr.request.call_id === call_id && tr.request.cseq === cseq) {
-              reply(482, JsSIP.c.REASON_482);
+              reply(482);
               return false;
             }
           }
@@ -89,7 +89,7 @@ JsSIP.sanityCheck = (function() {
           for(idx in ua.transactions.nist) {
             tr = ua.transactions.nist[idx];
             if(tr.request.from_tag === fromTag && tr.request.call_id === call_id && tr.request.cseq === cseq) {
-              reply(482, JsSIP.c.REASON_482);
+              reply(482);
               return false;
             }
           }
@@ -136,9 +136,9 @@ JsSIP.sanityCheck = (function() {
   }
 
   // Reply
-  function reply(status_code, reason_phrase) {
+  function reply(status_code) {
     var to,
-      response = "SIP/2.0 " + status_code + " " + reason_phrase + "\r\n",
+      response = "SIP/2.0 " + status_code + " " + JsSIP.c.REASON_PHRASE[status_code] + "\r\n",
       via_length = message.countHeader('via'),
       idx = 0;
 
diff --git a/src/Session.js b/src/Session.js
index 1786653d2..4f9d93a27 100644
--- a/src/Session.js
+++ b/src/Session.js
@@ -310,7 +310,7 @@ JsSIP.Session.prototype.receiveRequest = function(request) {
     // Transaction layer already responded 487 to the initial request.
 
     // Reply 200 to CANCEL
-    request.reply(200, JsSIP.c.REASON_200);
+    request.reply(200);
 
     /*
     * Terminate the whole session in case the user didn't accept nor reject the
@@ -332,7 +332,7 @@ JsSIP.Session.prototype.receiveRequest = function(request) {
         break;
       case JsSIP.c.BYE:
         if(this.status === JsSIP.c.SESSION_CONFIRMED) {
-          request.reply(200, JsSIP.c.REASON_200);
+          request.reply(200);
           this.ended('remote', request, JsSIP.c.causes.BYE);
         }
         break;
@@ -408,7 +408,7 @@ JsSIP.Session.prototype.receiveInitialRequest = function(ua, request) {
           return;
         }
 
-        request.reply(200, JsSIP.c.REASON_200, [
+        request.reply(200, JsSIP.c.REASON_PHRASE[200], [
           'Contact: <' + session.contact + '>'],
           sdp,
           // onSuccess
@@ -437,7 +437,7 @@ JsSIP.Session.prototype.receiveInitialRequest = function(ua, request) {
 
       onMediaFailure = function(e) {
         // Unable to get User Media
-        request.reply(486, JsSIP.c.REASON_486);
+        request.reply(486);
         session.failed('local', null, JsSIP.c.causes.USER_DENIED_MEDIA_ACCESS);
       };
 
@@ -446,7 +446,7 @@ JsSIP.Session.prototype.receiveInitialRequest = function(ua, request) {
         * peerConnection.setRemoteDescription throws an exception
         */
         console.log(JsSIP.c.LOG_SERVER_INVITE_SESSION +'PeerConnection Creation Failed: --'+e+'--');
-        request.reply(488, JsSIP.c.REASON_488);
+        request.reply(488);
         session.failed('remote', request, JsSIP.c.causes.BAD_MEDIA_DESCRIPTION);
       };
 
@@ -461,7 +461,7 @@ JsSIP.Session.prototype.receiveInitialRequest = function(ua, request) {
     */
     this.reject = function() {
       if (this.status === JsSIP.c.SESSION_WAITING_FOR_ANSWER) {
-        request.reply(486, JsSIP.c.REASON_486);
+        request.reply(486);
 
         this.failed('local', null, JsSIP.c.causes.REJECTED);
       }
@@ -474,12 +474,12 @@ JsSIP.Session.prototype.receiveInitialRequest = function(ua, request) {
     if (this.status !== JsSIP.c.SESSION_TERMINATED) {
       this.progress('local');
 
-      request.reply(180, JsSIP.c.REASON_180, [
+      request.reply(180, JsSIP.c.REASON_PHRASE[180], [
         'Contact: <' + this.contact + '>'
       ]);
     }
   } else {
-    request.reply(415, JsSIP.c.REASON_415);
+    request.reply(415);
   }
 };
 
@@ -639,7 +639,7 @@ JsSIP.Session.prototype.ackTimeout = function() {
 */
 JsSIP.Session.prototype.expiresTimeout = function(request) {
   if(this.status === JsSIP.c.SESSION_WAITING_FOR_ANSWER) {
-    request.reply(487, JsSIP.c.REASON_487);
+    request.reply(487);
 
     this.failed('system', null, JsSIP.c.causes.EXPIRES);
   }
@@ -660,7 +660,7 @@ JsSIP.Session.prototype.invite2xxRetransmission = function(retransmissions, requ
   if((retransmissions * JsSIP.Timers.T1) <= JsSIP.Timers.T2) {
     retransmissions += 1;
 
-    request.reply(200, JsSIP.c.REASON_200, [
+    request.reply(200, JsSIP.c.REASON_PHRASE[200], [
       'Contact: <' + this.contact + '>'],
       body);
 
@@ -678,7 +678,7 @@ JsSIP.Session.prototype.invite2xxRetransmission = function(retransmissions, requ
 * @private
 */
 JsSIP.Session.prototype.userNoAnswerTimeout = function(request) {
-  request.reply(408, JsSIP.c.REASON_408);
+  request.reply(408);
 
   this.failed('local',null, JsSIP.c.causes.NO_ANSWER);
 };
diff --git a/src/Transactions.js b/src/Transactions.js
index 336ef66ef..50674a0af 100644
--- a/src/Transactions.js
+++ b/src/Transactions.js
@@ -552,7 +552,7 @@ JsSIP.Transactions.InviteServerTransaction = function(request, ua) {
 
   this.reliableProvisionalTimer = null;
 
-  request.reply(100, JsSIP.c.REASON_100);
+  request.reply(100);
 };
 JsSIP.Transactions.InviteServerTransaction.prototype = new InviteServerTransactionPrototype();
 
@@ -622,13 +622,13 @@ JsSIP.Transactions.checkTransaction = function(ua, request) {
       tr = ua.transactions.ist[request.via_branch];
       if(tr) {
         if(tr.state === JsSIP.c.TRANSACTION_PROCEEDING) {
-          tr.request.reply(487, JsSIP.c.REASON_487);
+          tr.request.reply(487);
           return false;
         } else {
           return true;
         }
       } else {
-        request.reply_sl(481, JsSIP.c.REASON_481);
+        request.reply_sl(481);
         return true;
       }
       break;
diff --git a/src/UA.js b/src/UA.js
index 3e8525664..1ab54493b 100644
--- a/src/UA.js
+++ b/src/UA.js
@@ -362,7 +362,7 @@ JsSIP.UA.prototype.receiveRequest = function(request) {
   //Check that Ruri points to us
   if(request.ruri.user !== this.configuration.user) {
     console.log(JsSIP.c.LOG_UA +'Request URI does not point to us');
-    request.reply_sl(404, JsSIP.c.REASON_404);
+    request.reply_sl(404);
     return;
   }
 
@@ -384,13 +384,13 @@ JsSIP.UA.prototype.receiveRequest = function(request) {
    * They are processed as if they had been received outside the dialog.
    */
   if(method === JsSIP.c.OPTIONS) {
-    request.reply(200, JsSIP.c.REASON_200, [
+    request.reply(200, JsSIP.c.REASON_PHRASE[200], [
       'Allow: '+ JsSIP.utils.getAllowedMethods(this),
       'Accept: '+ JsSIP.c.ACCEPTED_BODY_TYPES
     ]);
   } else if (method === JsSIP.c.MESSAGE) {
     if (!this.checkEvent('newMessage') || this.listeners('newMessage').length === 0) {
-      request.reply(405, JsSIP.c.REASON_405, ['Allow: '+ JsSIP.utils.getAllowedMethods(this)]);
+      request.reply(405, JsSIP.c.REASON_PHRASE[405], ['Allow: '+ JsSIP.utils.getAllowedMethods(this)]);
       return;
     }
     message = new JsSIP.Message(this);
@@ -401,7 +401,7 @@ JsSIP.UA.prototype.receiveRequest = function(request) {
   if(!request.to_tag) {
     if(!this.registrator || (this.registrator && !this.registrator.registered)) {
       // High user does not want to be contacted
-      request.reply(410, JsSIP.c.REASON_410);
+      request.reply(410);
       return;
     }
 
@@ -416,7 +416,7 @@ JsSIP.UA.prototype.receiveRequest = function(request) {
         break;
       case JsSIP.c.BYE:
         // Out of dialog BYE received
-        request.reply(481, JsSIP.c.REASON_481);
+        request.reply(481);
         break;
       case JsSIP.c.CANCEL:
         session = this.findSession(request);
@@ -433,7 +433,7 @@ JsSIP.UA.prototype.receiveRequest = function(request) {
          */
         break;
       default:
-        request.reply(405, JsSIP.c.REASON_405);
+        request.reply(405);
         break;
     }
   }
@@ -459,7 +459,7 @@ JsSIP.UA.prototype.receiveRequest = function(request) {
      */
     else {
       if(method !== JsSIP.c.ACK) {
-        request.reply(481, JsSIP.c.REASON_481);
+        request.reply(481);
       }
     }
   }
diff --git a/src/constants.js b/src/constants.js
index 0d5bc35dd..b40e39842 100644
--- a/src/constants.js
+++ b/src/constants.js
@@ -130,68 +130,83 @@ JsSIP.c = {
   UPDATE:     'UPDATE',
   SUBSCRIBE:  'SUBSCRIBE',
 
-  // SIP Response Reasons
-
-  // Provisional
-  REASON_100: 'Trying',
-  REASON_180: 'Ringing',
-  REASON_181: 'Call Is Being Forwarded',
-  REASON_182: 'Queued',
-  REASON_183: 'Session Progress',
-
-  // Successful
-  REASON_200: 'OK',
-
-  // Redirection
-  REASON_300: 'Multiple Choices',
-  REASON_301: 'Moved Permanently',
-  REASON_302: 'Moved Temporarily',
-  REASON_305: 'Use Proxy',
-  REASON_380: 'Alternative Service',
-
-  // Request Failure
-  REASON_400: 'Bad Request',
-  REASON_401: 'Unauthorized',
-  REASON_402: 'Payment Required',
-  REASON_403: 'Forbidden',
-  REASON_404: 'Not Found',
-  REASON_405: 'Method Not Allowed',
-  REASON_406: 'Not Acceptable',
-  REASON_407: 'Proxy Authentication Required ',
-  REASON_408: 'Request Timeout',
-  REASON_410: 'Gone',
-  REASON_413: 'Request Entity Too Large',
-  REASON_414: 'Request-URI Too Long',
-  REASON_415: 'Unsupported Media Type',
-  REASON_416: 'Unsupported URI Scheme',
-  REASON_420: 'Bad Extension',
-  REASON_421: 'Extension Required',
-  REASON_423: 'Interval Too Brief',
-  REASON_480: 'Temporarily Unavailable',
-  REASON_481: 'Call/Transaction Does Not Exist',
-  REASON_482: 'Loop Detected',
-  REASON_483: 'Too Many Hops',
-  REASON_484: 'Address Incomplete',
-  REASON_485: 'Ambiguous',
-  REASON_486: 'Busy Here',
-  REASON_487: 'Request Terminated',
-  REASON_488: 'Not Acceptable Here',
-  REASON_491: 'Request Pending ',
-  REASON_493: 'Undecipherable',
-
-  // Server Failure
-  REASON_500: 'Server Internal Error',
-  REASON_501: 'Not Implemented',
-  REASON_502: 'Bad Gateway',
-  REASON_503: 'Service Unavailable',
-  REASON_504: 'Server Time-out',
-  REASON_505: 'Version Not Supported',
-  REASON_513: 'Message Too Large',
-
-  // Global Failure
-  REASON_600: 'Busy Everywhere',
-  REASON_603: 'Decline',
-  REASON_604: 'Does Not Exist Anywhere',
+  /* SIP Response Reasons
+   * DOC: http://www.iana.org/assignments/sip-parameters
+   * Copied from https://github.com/versatica/OverSIP/blob/master/lib/oversip/sip/constants.rb#L7
+   */
+  REASON_PHRASE: {
+    100: 'Trying',
+    180: 'Ringing',
+    181: 'Call Is Being Forwarded',
+    182: 'Queued',
+    183: 'Session Progress',
+    199: 'Early Dialog Terminated',  // draft-ietf-sipcore-199
+    200: 'OK',
+    202: 'Accepted',  // RFC 3265
+    204: 'No Notification',  //RFC 5839
+    300: 'Multiple Choices',
+    301: 'Moved Permanently',
+    302: 'Moved Temporarily',
+    305: 'Use Proxy',
+    380: 'Alternative Service',
+    400: 'Bad Request',
+    401: 'Unauthorized',
+    402: 'Payment Required',
+    403: 'Forbidden',
+    404: 'Not Found',
+    405: 'Method Not Allowed',
+    406: 'Not Acceptable',
+    407: 'Proxy Authentication Required',
+    408: 'Request Timeout',
+    410: 'Gone',
+    412: 'Conditional Request Failed',  // RFC 3903
+    413: 'Request Entity Too Large',
+    414: 'Request-URI Too Long',
+    415: 'Unsupported Media Type',
+    416: 'Unsupported URI Scheme',
+    417: 'Unknown Resource-Priority',  // RFC 4412
+    420: 'Bad Extension',
+    421: 'Extension Required',
+    422: 'Session Interval Too Small',  // RFC 4028
+    423: 'Interval Too Brief',
+    428: 'Use Identity Header',  // RFC 4474
+    429: 'Provide Referrer Identity',  // RFC 3892
+    430: 'Flow Failed',  // RFC 5626
+    433: 'Anonymity Disallowed',  // RFC 5079
+    436: 'Bad Identity-Info',  // RFC 4474
+    437: 'Unsupported Certificate',  // RFC 4744
+    438: 'Invalid Identity Header',  // RFC 4744
+    439: 'First Hop Lacks Outbound Support',  // RFC 5626
+    440: 'Max-Breadth Exceeded',  // RFC 5393
+    469: 'Bad Info Package',  // draft-ietf-sipcore-info-events
+    470: 'Consent Needed',  // RF C5360
+    478: 'Unresolvable Destination',  // Custom code copied from Kamailio.
+    480: 'Temporarily Unavailable',
+    481: 'Call/Transaction Does Not Exist',
+    482: 'Loop Detected',
+    483: 'Too Many Hops',
+    484: 'Address Incomplete',
+    485: 'Ambiguous',
+    486: 'Busy Here',
+    487: 'Request Terminated',
+    488: 'Not Acceptable Here',
+    489: 'Bad Event',  // RFC 3265
+    491: 'Request Pending',
+    493: 'Undecipherable',
+    494: 'Security Agreement Required',  // RFC 3329
+    500: 'Server Internal Error',
+    501: 'Not Implemented',
+    502: 'Bad Gateway',
+    503: 'Service Unavailable',
+    504: 'Server Time-out',
+    505: 'Version Not Supported',
+    513: 'Message Too Large',
+    580: 'Precondition Failure',  // RFC 3312
+    600: 'Busy Everywhere',
+    603: 'Decline',
+    604: 'Does Not Exist Anywhere',
+    606: 'Not Acceptable'
+  },
 
   // SIP Attributes
   MAX_FORWARDS: 69,