Why does my unlocked T-Mobile phone have difficulty receiving data using AT&T?

[Rick Lowrance]

Hi. First post here.

I have a Galaxy S3 mini, model number SGH-T399. It is a factory unlocked T-Mobile phone and I have an ATT sim card in it.

The phone will not receive data in my home area. It also will not receive data in Denver or Billings. Strangely, it DOES receive data beautifully in Atlanta.

Tech support at AT&T told me the problem is that it is a T-Mobile phone.

Does this make sense? It might also be a problem with the phone. I don't want to sell the phone if it is defective. I would like to try to figure out a way to determine if the phone is, for certain, working properly.

Thanking anyone in advance if they take the time to answer this.

 

[Rukbat]

The phone will not receive data in my home area. It also will not receive data in Denver or Billings. Strangely, it DOES receive data beautifully in Atlanta.

Tech support at AT&T told me the problem is that it is a T-Mobile phone.

Does this make sense?

Absolutely. AT&T different frequency bands for 3G and 4G than TMobile does. In some markets, the TMobile frequency that the phone can handle happens to be the one AT&T is using in that market. Some phones are interchangeable between carriers with no problem, some aren't - the S3, in the markets you're using it in, isn't. (You should still receive 2G data, unless AT&T has completely reworked Denver and Billings and there's no 2G data there any more. (And if you did get it, you'd get old waiting for a web page to load - that's the speed we were using 10 years ago and more.)

There's no way to "fix" it, any more than there's a way to "fix" your car not flying. The phone wasn't made to use data on AT&T's network. (If someone in your area is using an AT&T S3 on TMobile, maybe an ad in Craig's List could get you together for a phone swap - he'd be having problems too.)