BYOD for existing accounts

As long as you keep paying installments, you can use a different phone by moving the sim card. 

There is no fee for doing this yourself. 

Just make sure you're using a phone that is acceptable and capable of working on AT&t after the 3-g shutdown or are you likely have suspended service now for trying to use an incompatible phone.

Hello Khi469, we would be glad to answer your question about BYOD.

You would need to pay the installment off on your current device. If you switch devices, AT&T will request a one time payment for the balance of the installment. Also, you will lose any promotional credits that you are receiving.

Let us know if you have any further questions or concerns.

Thank you for visiting AT&T Community Forums.

Carlton, AT&T Community Specialist

I broke my phone. My at XIAOMI, sent me a new compatible phone. I went to my local store, and the manager blew me off and told me to call. My friend programmed it. It sees the network, but instantly hangs up. Any solutions?  Thanks!

@RIKtheGEEK 

get a compatible phone that brand does not work on ATT.

@RIKtheGEEK

Ar&t will not allow that brand.  They will suspend service until you replace it.

https://www.att.com/buy/byod/identify?devicetype=phone

These work... 

Service capabilities of unlocked devices https://www.att.com/ecms/dam/att/consumer/help/pdf/Service-Capabilities-Unlocked-Devices-ATT-Network.pdf