Activating unlocked iphone 6 on AT&T

[Phonesurfer]

I preordered a tmobile iphone 6 on apple store to replace my iphone 4. i am hoping the tmobile iphone 6 purchased from apple is unlocked (I have read conflicting info on this). i am currently using the iphone 4 on AT&T . If the tmobile phone is unlocked (I hope it is) and I want to use it in place of my iphone 4 on AT&T, how would I go about setting up the iphone 6 with my iphone 4 phone number? I have read about switching sims to activate, but the iphone 4 has a different sim than the iphone 6.... Would I purchase a new sim from AT&T to put in the iphone 6? If so, how would the phone number from the iphone 4 get transferred over to the iphone 6?
Thanks

 

[Applejuiced]

You just go to att and ask them to give you a nanosim with your phone number to replace your current microsim.
Put it in the new phone and you're done.

 

[Dreday24]

http://www.amazon.com/gp/product/B009QTVG4K/ref=oh_aui_detailpage_o04_s01?ie=UTF8&psc=1

 

[Phonesurfer]

Thanks for the replies... Now all I need is an unlocked phone