Can I use someone else's upgrade?

[Allora]

My grandpa is eligible for an upgrade but he's fine with his phone and is okay with me using his upgrade. I paid him to get the iPhone 6 for me, but the phone is now in his number (His old phone is deactivated now or something).

Can I go to the AT&T store and ask them to switch the sim card from my iPhone 4 to the iPhone 6, and ask them to activate my grandpa's old phone again?

 

[PsyOpWarlord]

yes you can do that at the ATT store. Take your grandfather and both phones.

 

[Applejuiced]

Yes. People do it all the time.
Explain to the att store about the swap so they can remove any iPhone data plan from his line and switch with compatible sims.