Hi there!
I have been using my Fairphone 3 in the DC area and around Maryland since March 2020. I have TMobile and I get excellent service as well as 4G. The phone has been performing great, and I am really glad to have one. There are some slight quirks I have noticed:
The phone gets very warm when being used for long periods of time (even inside a room with AC)
Sometimes Google Photos lags or the camera wont save the pictures that were just captured
The battery gets very warm (40 C) while being charged
other than that, I love the green Fairphone case and the Fairphone 3
