I received my new AT&T phone today and I haven't powered it up. I did sign up for AT&T non-contract service. I want to unlock it for use in T-mobile, as I have T-mobile now. However, I am confused as to how to get the $650 credit and unlock the phone. Per wiki and Citi, I need to "activate and maintain the service..". But, then to unlock the phone, I can't activate it on AT&T. So, do I unlock first, then activate AT&T service for 15 days???

Per Wiki:
Make your phone purchase using your unique phone offer link (which will be provided to you), activate and maintain service with AT&T for 15 days. If you buy a new phone now it will count toward the $2,000 in qualifying purchases!

2. How do I unlock the phone to move it off of AT&T?

Do not power up the phone, insert SIM card, or activate phone. Go through the unlock portal as a non-AT&T customer and request unlock code. The IMEI can be located on the box. The unlock instructions email should arrive within 24 hours. See post 716 for detailed unlocking instructions.