Actually the Visual Voicemail is based on the SIM card that comes with the iphone. At least that is what I have read. I unlocked my iphone to use it with my corporate at&t account. If you don't unlock it you are not only stuck with att but you have to use their apple specific accounts. That is how apple gets paid from att, they get a cut of all apple/att accounts. Visual voicemail looks cool but I'd rather use my existing account.