Audiovox CDM-8940

I understand how to set my 8940 to vibrate-and-then-ring for phone calls. But does anyone know if I can make it vibrate instead of ring for SMS message receive and for voicemail notifications?

I tested it this morning and all I could make it do was assign one of my ringers (the tones or download tones) to SMS message receive and voicemail. I'm used to being able to select vibrate instead of audio ring for these items.

Thanks in advance...