I just got my iPhone setup on T-Mobile but I can't figure out how to get voicemail working. Every time I go to the phone app and hit the voicemail button, it gives me a busy signal. Same thing if I hold down "1". When I dial "123", it asks to setup my mailbox and asks for my 10-digit number, but every time I put in my phone number it says my mailbox number is invalid. Anybody know how I can get this working?