diff --git a/apps/app_voicemail.c b/apps/app_voicemail.c
index b0fed2d4765dabc0d01176b679cccbfa3a6dcd4d..635d6fe95df77bb7c4d558c0eacb3be5c592d936 100644
--- a/apps/app_voicemail.c
+++ b/apps/app_voicemail.c
@@ -522,6 +522,7 @@ static char *descrip_vm =
 	"             the greeting.  Context defaults to the current context.\n"
 	"    g(#) - Use the specified amount of gain when recording the voicemail\n"
 	"           message. The units are whole-number decibels (dB).\n"
+	"           Only works on supported technologies, which is Zap only.\n"
 	"    s    - Skip the playback of instructions for leaving a message to the\n"
 	"           calling party.\n"
 	"    u    - Play the 'unavailable' greeting.\n"