AT&T LG G3 does 4G LTE on T-Mobile

Mom switched to T-Mobile today. My AT&T LG G3 does 4G LTE on T-Mobile. Speed test said around 20 Mbps, faster then my Comcast connection. I think I got 40 Mbps on AT&T.

I had to manually add an APN. Nothing worked until I added the APN.