Motorola

I recently became a T-mobile subscriber and have an odd problem. My RAZR V3 and V3i notify me of new voicemails with text messages containing strange symbols (@, *, etc.) I don't get voicemail notification with these phones, only weird text messages. I tried a few different t-mobile SIM cards; all had the same result. Strange thing is the moto's only do this with a T-mobile SIM card inserted. If I use a Cingular SIM card I receive voicemail notification properly in both phones. How do I receive voicemail notification, rather than text messages when I receive a new voicemail? If it helps, both of my RAZR's are factory direct, unbranded, and unlocked. Any feedback would be greatly appreciated.