Not able to receive or make calls.

We'll be happy to assist you @Mbs5678, with not being able to make or receive calls.

AT&T has recently improved the network to better accommodate next generation technologies and services by sun-setting the 3G coverage. There is a list that will provide you with all devices that will still be supported on AT&T's upgraded network. If your device is compatible but is not connecting, the following may resolve the issues:

• Program the data settings for your non-AT&T device
• Download the latest software – If you are an AT&T Customer, software downloads are automatic. If you have a non-branded device, you will need to go directly to the manufacturer.
• Make sure 4G is enabled on your device. Some customers disable 4G.

First: Determine if the device is "HD Voice-capable" (a.k.a "Volte" or "Voice over LTE")

• If no, you will need an HD Voice-capable device
• If yes, but not AT&T branded, you may need to update the device software.

Apple- based on IOS version:

• Settings>Cellular>Cellular Data Options>Voice & Data>LTE (select LTE option)
• Settings>Cellular>Cellular Data Options>Enable LTE (select LTE option)

Android:

• Go to Settings>Connection>Mobile networks>Enhanced LTE services and select on.

Give these tips a try and let us know how they worked out for you!

Ashley, AT&T Community Specialist 

Check imei

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

If it says no, you can't use the phone on at&t