You can either have AT&T assign you a new phone number for your iPhone or transfer your existing phone number to AT&T for use with your iPhone.
If you want a new phone number, simple click continue when the Tranfer Your Mobile Number screen appears.
If you want to transfer your current number, fill out the form with your current number, the account number from your previous phone provider, your billing zip code, and your account password, if you have one.
Click continue.
If you are transferring your number, AT&T will check to make sure that the number can be transferred. Most numbers can be transferred, but some cannot (Learn more about why some numbers cannot be transferred to iPhone).
When your number transfer is registered, iTunes will prompt you to continue. Number transfers can take up to 6 hours to complete. While you wait, you will be also to use the iPhone and make outgoing calls, but not receive calls.
