Solving “No Carrier” Problems with T-Mobile in iOS 10
Peter Cohen reports that many T-Mobile customers who updated an iPhone 6, iPhone 6 Plus, or iPhone SE to iOS 10 suddenly had trouble getting cell service on their phones. Power cycling the iPhone fixed the problem temporarily, but if you’re suffering from this bug, you can now eliminate the error permanently with a carrier update from T-Mobile. Apply it by going to Settings > General > About.
I tried the fix for my iPhone 6+. It did not work. I called T-Mobile, and they told me to be patient: Apple is going to fix it. Not yet!
Carrier settings updated, everything else up to date - same problem. phone only works on wifi now.
Sorry to hear it, guys! Sounds like there may be multiple things going on. :-(