Can i use a prepaid sim kit to activate an AT&T iPhone 6, that is on installment plan and not paid off?

[Tp9053]

Activate iPhone with prepaid sim

 

[Saga Lout]

It won't work.

Your Service Provider won't allow a change of SIM without the existing provider issuing you a PUK - Personal Unlocking Key - to show you aren't in contract and you don't don't owe them any money.