Amazon follows AT&T rules. You can keep the same number. The important part to note is if your account is eligible for an upgrade, meaning you have completed your previous 2 year contract. There is a button to check for "upgrade eligibility" on the Samsung Focus page on Amazon. Once you have verified eligibility, just select "service type" and it will take you through a series of pages allowing you to choose from the available services (voice, messaging, data plans, etc.). Once completed you will receive a confirmation email. When you get the phone, you need to call AT&T to activate your new SIM card. Verify with the AT&T rep that they have added the correct services to your account. Boom your done.