Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 80572)
+++ channels/chan_sip.c	(working copy)
@@ -12873,8 +12873,17 @@
 	transferer->readformat = chan2->readformat;
 	transferer->writeformat = chan2->writeformat;
 
-	/* Prepare for taking over the channel */
+	/* Prepare for taking over the channel.  Go ahead and grab this channel
+	 * lock here to avoid a deadlock with callbacks into the channel driver
+	 * that hold the channel lock and want the pvt lock.  */
+	while (ast_channel_trylock(chan2)) {
+		struct sip_pvt *pvt = chan2->tech_pvt;
+		ast_mutex_unlock(&pvt->lock);
+		usleep(1);
+		ast_mutex_lock(&pvt->lock);
+	}
 	ast_channel_masquerade(transferer, chan2);
+	ast_channel_unlock(chan2);
 
 	/* Setup the extensions and such */
 	ast_copy_string(transferer->context, chan2->context, sizeof(transferer->context));