diff -urb asterisk-1.6.1.4/channels/chan_dahdi.c asterisk-new-1.6.1.4/channels/chan_dahdi.c
--- asterisk-1.6.1.4/channels/chan_dahdi.c	2009-10-01 18:51:27.000000000 +0400
+++ asterisk-new-1.6.1.4/channels/chan_dahdi.c	2009-10-01 19:07:31.000000000 +0400
@@ -8367,7 +8367,7 @@
 					if (last) {
 						if (!last->mwisendactive &&	 last->sig & __DAHDI_SIG_FXO) {
 							res = has_voicemail(last);
-							if (last->msgstate != res) {
+							if (last->msgstate != res && res > 0) {
 
 								/* This channel has a new voicemail state,
 								* initiate a thread to send an MWI message