You can do a (LNP) port of your number from T-Mobile to AT&T as long as the number you have is still local to where you are using it (FCC Guidelines & Requirement), as for your T-Mobile account If you terminate your Service, your termination will be effective at the end of your current billing cycle, and you will remain responsible for all fees and Charges for your Service and usage through the end of that billing cycle. Info Source
You must provide the following account information as it appears on record with your current service provider:
Name of the account holder
PIN or password (if applicable)
AT&T will contact your current service provider to complete the transfer. The information you provide must exactly match your current service provider's records. If there is a mismatch in the data, the transfer will be delayed.
Q. How does a number transfer work? A. The transfer process varies slightly depending on how you decide to purchase and receive your new AT&T phone. You may choose to visit an AT&T retail store or you can order online and have it shipped directly to you. The processes for both options are outlined below:
AT&T retail store: AT&T will send a number transfer request to your current service provider and wait for confirmation to transfer the number. Meanwhile, your AT&T handset will be activated into mixed service. You will be able to make calls on your new AT&T handset but will continue to receive calls on your old handset until the number transfer is complete. Once AT&T receives confirmation, your activation will be complete, allowing you to make and receive calls on your AT&T handset. Your old service provider will be notified that you have activated service with AT&T and will automatically cancel your account.
Order online: AT&T will send a number transfer request to your current service provider and wait for confirmation to transfer the number. Once transfer confirmation is received your AT&T phone will be shipped. Your existing phone will continue to work until you receive your AT&T phone and activate it. Once your AT&T account is activated, your old service provider will be notified of your new service with AT&T and will cancel your account.
Ok, so I just got off the phone with an AT&T representative. She told me that I can go ahead and pre-order the phone and put in a request to port my current number because the actual process of them requesting the number doesn't happen until I activate my new phone. So if I were to receive my phone in the mail before November 3rd (tmo contract end date), I can just hold onto it and activate it after the 3rd so I don't incur a termination fee with T-mobile.