diff -ur asterisk/channels/chan_sip.c asterisk-work/channels/chan_sip.c
--- asterisk/channels/chan_sip.c	2004-12-31 17:43:04.000000000 +0800
+++ asterisk-work/channels/chan_sip.c	2005-02-04 14:19:42.261761368 +0800
@@ -321,6 +321,7 @@
 	int tag;				/* Another random number */
 	int sessionid;				/* SDP Session ID */
 	int sessionversion;			/* SDP Session Version */
+	int intercom;				/* Whether this is an intercom call */
 	struct sockaddr_in sa;			/* Our peer */
 	struct sockaddr_in redirip;		/* Where our RTP should be going if not to us */
 	struct sockaddr_in vredirip;		/* Where our Video RTP should be going if not to us */
@@ -1398,12 +1399,17 @@
 		ast_log(LOG_WARNING, "sip_call called on %s, neither down nor reserved\n", ast->name);
 		return -1;
 	}
-	/* Check whether there is vxml_url, distinctive ring variables */
 
+	/* Check whether there is vxml_url, distinctive ring variables, or intercom */
 	headp=&ast->varshead;
 	AST_LIST_TRAVERSE(headp,current,entries) {
-		/* Check whether there is a VXML_URL variable */
-		if (!vxml_url && !strcasecmp(ast_var_name(current),"VXML_URL")) {
+		if (!p->intercom && !strcasecmp(ast_var_name(current),"INTERCOM")) {
+			/* Check whether there is a INTERCOM variable */
+		  	if (!strcasecmp(ast_var_value(current), "true"))  {
+				p->intercom = 1;
+			}
+		} else if (!vxml_url && !strcasecmp(ast_var_name(current),"VXML_URL")) {
+			/* Check whether there is a VXML_URL variable */
 			vxml_url = ast_var_value(current);
 		} else if (!distinctive_ring && !strcasecmp(ast_var_name(current),"ALERT_INFO")) {
 			/* Check whether there is a ALERT_INFO variable */
@@ -2273,6 +2279,7 @@
 	memset(p, 0, sizeof(struct sip_pvt));
         ast_mutex_init(&p->lock);
 
+	p->intercom = 0;
 	p->initid = -1;
 	p->autokillid = -1;
 	p->stateid = -1;
@@ -3668,7 +3675,7 @@
 	char invite[256]="";
 	char from[256];
 	char to[256];
-	char tmp[80];
+	char tmp[256];
 	char iabuf[INET_ADDRSTRLEN];
 	char *l = default_callerid, *n=NULL;
 	int x;
@@ -3740,7 +3747,13 @@
 	} else {
 		snprintf(invite, sizeof(invite), "sip:%s%s", p->tohost, urioptions);
 	}
 	strncpy(p->uri, invite, sizeof(p->uri) - 1);
+	/* If there is an intercom request append it */
+	if (p->intercom)
+	{
+		snprintf(tmp, sizeof(tmp), "%s;intercom=true", invite);
+		snprintf(invite, sizeof(invite), "%s", tmp);
+	}
 	/* If there is a VXML URL append it to the SIP URL */
 	if (vxml_url)
 	{