diff --git a/callerid.c b/callerid.c
index 68b42f8d4335b66b199d6952c314858d02401249..58891d0fab0aa5bd33f2baac6154af44a4ec65aa 100644
--- a/callerid.c
+++ b/callerid.c
@@ -905,21 +905,42 @@ void ast_shrink_phone_number(char *n)
 	n[y] = '\0';
 }
 
-/*! \brief checks if string consists only of digits and * \# and + 
-	\return 1 if string is valid AST phone number
-	\return 0 if not
+/*! \brief Checks if phone number consists of valid characters 
+	\param exten	String that needs to be checked
+	\param valid	Valid characters in string
+	\return 1 if valid string, 0 if string contains invalid characters
 */
-int ast_isphonenumber(char *n)
+static int ast_is_valid_string(const char *exten, const char *valid)
 {
 	int x;
-	if (ast_strlen_zero(n))
+
+	if (ast_strlen_zero(exten))
 		return 0;
-	for (x=0;n[x];x++)
-		if (!strchr("0123456789*#+", n[x]))
+	for (x=0; exten[x]; x++)
+		if (!strchr(valid, exten[x]))
 			return 0;
 	return 1;
 }
 
+/*! \brief checks if string consists only of digits and * \# and + 
+	\return 1 if string is valid AST phone number
+	\return 0 if not
+*/
+int ast_isphonenumber(const char *n)
+{
+	return ast_is_valid_string(n, "0123456789*#+");
+}
+
+/*! \brief checks if string consists only of digits and ( ) - * \# and + 
+	Pre-qualifies the string for ast_shrink_phone_number()
+	\return 1 if string is valid AST shrinkable phone number
+	\return 0 if not
+*/
+int ast_is_shrinkable_phonenumber(const char *exten)
+{
+	return ast_is_valid_string(exten, "0123456789*#+()-.");
+}
+
 /*! \brief parse string for caller id information 
 	\return always returns 0, as the code always returns something.
   XXX note that 'name' is not parsed consistently e.g. we have
diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index c16817dfa8879c2053014384a87ca03e33793e1a..4ce8a121f19ee048818bd04cefef6beb613b6ea7 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -7234,7 +7234,8 @@ static int check_user_full(struct sip_pvt *p, struct sip_request *req, int sipme
 			*c = '\0';
 		tmp = ast_strdupa(of);
 		if (tmp) {
-			ast_shrink_phone_number(tmp);
+			if (ast_is_shrinkable_phonenumber(tmp))
+				ast_shrink_phone_number(tmp);
 			ast_string_field_set(p, cid_num, tmp);
 		} else {
 			ast_string_field_set(p, cid_num, of);
@@ -7265,7 +7266,8 @@ static int check_user_full(struct sip_pvt *p, struct sip_request *req, int sipme
 				ast_string_field_set(p, cid_name, calleridname);
 			tmp = ast_strdupa(rpid_num);
 			if (tmp) {
-				ast_shrink_phone_number(tmp);
+				if (ast_is_shrinkable_phonenumber(tmp))
+					ast_shrink_phone_number(tmp);
 				ast_string_field_set(p, cid_num, tmp);
 			} else {
 				ast_string_field_set(p, cid_num, rpid_num);
@@ -7301,7 +7303,8 @@ static int check_user_full(struct sip_pvt *p, struct sip_request *req, int sipme
 			if (!ast_strlen_zero(user->cid_num) && !ast_strlen_zero(p->cid_num)) {
 				char *tmp = ast_strdupa(user->cid_num);
 				if (tmp) {
-					ast_shrink_phone_number(tmp);
+					if (ast_is_shrinkable_phonenumber(tmp))
+						ast_shrink_phone_number(tmp);
 					ast_string_field_set(p, cid_num, tmp);
 				} else {
 					ast_string_field_set(p, cid_num, user->cid_num);
@@ -7376,7 +7379,8 @@ static int check_user_full(struct sip_pvt *p, struct sip_request *req, int sipme
 				if (*calleridname)
 					ast_string_field_set(p, cid_name, calleridname);
 				if (tmp) {
-					ast_shrink_phone_number(tmp);
+					if (ast_is_shrinkable_phonenumber(tmp))
+						ast_shrink_phone_number(tmp);
 					ast_string_field_set(p, cid_num, tmp);
 				} else {
 					ast_string_field_set(p, cid_num, rpid_num);
@@ -7430,7 +7434,8 @@ static int check_user_full(struct sip_pvt *p, struct sip_request *req, int sipme
 				if (!ast_strlen_zero(peer->cid_num) && !ast_strlen_zero(p->cid_num)) {
 					char *tmp = ast_strdupa(peer->cid_num);
 					if (tmp) {
-						ast_shrink_phone_number(tmp);
+						if (ast_is_shrinkable_phonenumber(tmp))
+							ast_shrink_phone_number(tmp);
 						ast_string_field_set(p, cid_num, tmp);
 					} else {
 						ast_string_field_set(p, cid_num, peer->cid_num);
diff --git a/include/asterisk/callerid.h b/include/asterisk/callerid.h
index 066dc7888d77ceca6a29eb9d2bf4788c5e6233db..a49d686abffb350dfa016c291817ceaab77870bb 100644
--- a/include/asterisk/callerid.h
+++ b/include/asterisk/callerid.h
@@ -193,11 +193,18 @@ extern int ast_gen_cas(unsigned char *outbuf, int sas, int len, int codec);
  */
 extern void ast_shrink_phone_number(char *n);
 
-/*! \brief Check if a string consists only of digits.   
+/*! \brief Check if a string consists only of digits and + \#
     \param n number to be checked.
     \return Returns 0 if n is a number, 1 if it's not.
  */
-extern int ast_isphonenumber(char *n);
+extern int ast_isphonenumber(const char *n);
+
+/*! \brief Check if a string consists only of digits and and + \# ( ) - .
+	(meaning it can be cleaned with ast_shrink_phone_number)
+    \param exten The extension (or URI) to be checked.
+    \return Returns 0 if n is a number, 1 if it's not.
+ */
+extern int ast_is_shrinkable_phonenumber(const char *exten);
 
 extern int ast_callerid_split(const char *src, char *name, int namelen, char *num, int numlen);