How much is the new tmobile iphone?

Ok so i had the iphone 4s with at&t on my moms side but she took it away for a long time, and i want a phone again.since my dad is nicer and he has t mobile, i want to switch to his plan and get an iphone 5 with tmobile, he is willing to do that, andi would be getting a nice new phone out of it, except how much would it to be to get a new iphone 5 with tmobile, and would it cost anything since i would be switching from at&t to tmobile?

I think new customers get them free. If not a 16gb iPhone 5 retails for about $899.99. Plus activation fee. So about $1k to switch if its not free.