If I have a unlocked Cingular V551, and set up an account with T-Mobile AND Cingular prepaid, using each companies SIM card. Will I have a different phone number for each ?? If it's even possible to do that. My phone used to work with my TomTom. Now it won't, and the TomTom support says that if I used Cingular instead of T-Mobile, it would again be compatable. Thanks.