I used to get T-Mobile when I dialed 611 on my att phone for support. It turned out the nearest lte cell tower was owned by T-Mobile and they had a treaty for tower sharing in locales where att had no coverage. OR You could try a 'reset network settings' which seems to have solved some network issues I was having.
Yep. What is happening is basically what PhilESK is saying. The nearest tower your phone is connected to happens to be owned by Verizon and your Carrier (att) has a treaty with Verizon where they share that specific tower. That way your carrier can have coverage in that area.
