diff -Naur asterisk-1.0.7-clean/channels/chan_zap.c asterisk-1.0.7-clean-patched/channels/chan_zap.c
--- asterisk-1.0.7-clean/channels/chan_zap.c	2005-02-25 19:11:41.000000000 +0100
+++ asterisk-1.0.7-clean-patched/channels/chan_zap.c	2005-06-15 11:46:57.000000000 +0200
@@ -237,6 +237,7 @@
 static int cur_debounce = -1;
 
 static int priindication_oob = 0;
+static int handleprogresscause = 0;
 
 #ifdef ZAPATA_PRI
 static int minunused = 2;
@@ -516,6 +517,7 @@
 	int busycount;
 	int callprogress;
 	int priindication_oob;
+	int handleprogresscause;
 	struct timeval flashtime;	/* Last flash-hook time */
 	struct ast_dsp *dsp;
 	int cref;					/* Call reference number */
@@ -6474,6 +6476,7 @@
 		tmp->restrictcid = restrictcid;
 		tmp->use_callingpres = use_callingpres;
 		tmp->priindication_oob = priindication_oob;
+		tmp->handleprogresscause = handleprogresscause;
 		if (tmp->usedistinctiveringdetection) {
 			if (!tmp->use_callerid) {
 				ast_log(LOG_NOTICE, "Distinctive Ring detect requires 'usecallerid' be on\n");
@@ -7743,11 +7746,25 @@
 				if (chanpos > -1) {
 					if (pri->overlapdial && !pri->pvts[chanpos]->proceeding) {
 						struct ast_frame f = { AST_FRAME_CONTROL, AST_CONTROL_PROGRESS, };
-						
+
+						/* handle cause code 'user busy' (17) in q.931 PROGRESS messages*/
+						if (e->proceeding.cause > -1) {
+							if (option_verbose > 2) 
+								ast_verbose(VERBOSE_PREFIX_3 "PROGRESS with cause code %d receiveded!\n",e->proceeding.cause);
+							if ( handleprogresscause && (e->proceeding.cause == AST_CAUSE_USER_BUSY)) {
+								if (pri->pvts[chanpos]->owner) {
+									if (option_verbose > 2) 
+										ast_verbose(VERBOSE_PREFIX_3 "PROGRESS with 'user busy' received, signaling AST_CONTROL_BUSY instead of AST_CONTROL_PROGRESS\n");
+									pri->pvts[chanpos]->owner->hangupcause = e->proceeding.cause;
+									f.subclass = AST_CONTROL_BUSY;
+								}
+							}
+						}
+
 						ast_mutex_lock(&pri->pvts[chanpos]->lock);
 						ast_log(LOG_DEBUG, "Queuing frame from PRI_EVENT_PROGRESS on channel %d/%d span %d\n",
 								pri->pvts[chanpos]->logicalspan, pri->pvts[chanpos]->prioffset,pri->span);
-							zap_queue_frame(pri->pvts[chanpos], &f, pri);
+						zap_queue_frame(pri->pvts[chanpos], &f, pri);
 						ast_mutex_unlock(&pri->pvts[chanpos]->lock);
 					}
 				}
@@ -9511,6 +9528,13 @@
 			else
 				ast_log(LOG_WARNING, "'%s' is not a valid pri indication value, should be 'inband' or 'outofband' at line %d\n",
 					v->value, v->lineno);
+ 		} else if (!strcasecmp(v->name, "handleprogresscause")) {
+ 			if (!strcasecmp(v->value, "yes"))
+ 				handleprogresscause = 1;
+ 			else if (!strcasecmp(v->value, "no"))
+ 				handleprogresscause = 0;
+ 			else
+ 			    ast_log(LOG_WARNING, "'%s' is not a valid value for 'handleprogresscause', should be 'yes' or 'no' at line %d\n",v->value, v->lineno);
 		} else if (!strcasecmp(v->name, "minunused")) {
 			minunused = atoi(v->value);
 		} else if (!strcasecmp(v->name, "idleext")) {
diff -Naur asterisk-1.0.7-clean/configs/zapata.conf.sample asterisk-1.0.7-clean-patched/configs/zapata.conf.sample
--- asterisk-1.0.7-clean/configs/zapata.conf.sample	2004-12-30 21:36:57.000000000 +0100
+++ asterisk-1.0.7-clean-patched/configs/zapata.conf.sample	2005-06-14 17:19:12.000000000 +0200
@@ -90,6 +90,13 @@
 ;
 ; priindication = outofband
 ;
+; Handle cause code in PROGRESS message
+; Some Telco send PROGRESS messages with a cause code to signal
+; certain line conditions, e.g. user busy.
+; Turn this option to enable busy detection in PROGRESS messages.
+; Default = no
+;
+;handleprogresscause=yes
 ;
 ; Signalling method (default is fxs).  Valid values:
 ; em:      E & M