--- asterisk-1.4.22/channels/chan_sip.c	2008-09-08 23:10:10.000000000 +0200
+++ asterisk-1.4.22-patched/channels/chan_sip.c	2009-01-15 10:00:56.000000000 +0100
@@ -1410,6 +1410,7 @@
 static int function_sipchaninfo_read(struct ast_channel *chan, char *cmd, char *data, char *buf, size_t len);
 static int sip_dtmfmode(struct ast_channel *chan, void *data);
 static int sip_addheader(struct ast_channel *chan, void *data);
+static int sip_removeheader(struct ast_channel *chan, void *data);
 static int sip_do_reload(enum channelreloadreason reason);
 static int sip_reload(int fd, int argc, char *argv[]);
 static int acf_channel_read(struct ast_channel *chan, char *funcname, char *preparse, char *buf, size_t buflen);
@@ -18165,6 +18193,26 @@
 "Adding the wrong headers may jeopardize the SIP dialog.\n"
 "Always returns 0\n";
 
+static char *app_sipremoveheader = "SIPRemoveHeader";
+static char *synopsis_sipremoveheader = "Remove SIP headers previously added with SIPAddHeader";
+
+static char *descrip_sipremoveheader = ""
+"  SIPRemoveHeader()\n"
+"SIPRemoveHeader() allows you to remove headers which were previously \n"
+"added with SIPAddHeader(). If no parameter is supplied, all previously \n"
+"added headers will be removed. If a parameter is supplied, only the matching \n"
+"headers will be removed.\n\n"
+"For example you have added these 2 headers:\n"
+"  SIPAddHeader(P-Asserted-Identity: sip:foo@bar);\n"
+"  SIPAddHeader(P-Preferred-Identity: sip:bar@foo);\n\n"
+"  // remove all headers\n"
+"  SIPRemoveHeader();\n\n"
+"  // remove all P- headers\n"
+"  SIPRemoveHeader(P-);\n\n"
+"  // remove only the PAI header (note the : at the end)\n"
+"  SIPRemoveHeader(P-Asserted-Identity:);\n\n"
+"Always returns 0\n";
+
 
 /*! \brief Set the DTMFmode for an outbound SIP call (application) */
 static int sip_dtmfmode(struct ast_channel *chan, void *data)
@@ -18255,6 +18303,38 @@
 	return 0;
 }
 
+/*! \brief Remove SIP headers added previously with SipAddHeader application */
+static int sip_removeheader(struct ast_channel *chan, void *data)
+{
+	struct ast_var_t *newvariable;
+	struct varshead *headp;
+	int removeall = 0;
+	char *inbuf = (char *) data;
+	
+	if (ast_strlen_zero(inbuf)) {
+		removeall = 1;
+	}
+	ast_channel_lock(chan);
+
+	headp=&chan->varshead;
+	AST_LIST_TRAVERSE_SAFE_BEGIN (headp, newvariable, entries) {
+		if (strncasecmp(ast_var_name(newvariable), "SIPADDHEADER", strlen("SIPADDHEADER")) == 0) {
+			if (removeall || (!strncasecmp(ast_var_value(newvariable),inbuf,strlen(inbuf)))) {
+				if (sipdebug)
+					ast_log(LOG_DEBUG,"removing SIP Header \"%s\" as %s\n", 
+						ast_var_value(newvariable), 
+						ast_var_name(newvariable));
+				AST_LIST_REMOVE_CURRENT(headp, entries);
+				ast_var_delete(newvariable);
+			}
+		}
+	}
+	AST_LIST_TRAVERSE_SAFE_END;
+
+	ast_channel_unlock(chan);
+	return 0;
+}
+
 /*! \brief Transfer call before connect with a 302 redirect
 \note	Called by the transfer() dialplan application through the sip_transfer()
 	pbx interface function if the call is in ringing state 
@@ -18565,6 +18645,7 @@
 	/* Register dialplan applications */
 	ast_register_application(app_dtmfmode, sip_dtmfmode, synopsis_dtmfmode, descrip_dtmfmode);
 	ast_register_application(app_sipaddheader, sip_addheader, synopsis_sipaddheader, descrip_sipaddheader);
+	ast_register_application(app_sipremoveheader, sip_removeheader, synopsis_sipremoveheader, descrip_sipremoveheader);
 
 	/* Register dialplan functions */
 	ast_custom_function_register(&sip_header_function);
@@ -18604,6 +18685,7 @@
 	/* Unregister dial plan applications */
 	ast_unregister_application(app_dtmfmode);
 	ast_unregister_application(app_sipaddheader);
+	ast_unregister_application(app_sipremoveheader);
 
 	/* Unregister CLI commands */
 	ast_cli_unregister_multiple(cli_sip, sizeof(cli_sip) / sizeof(struct ast_cli_entry));