I had an issue after updating my 1020 from 8.1 dev preview build (I believe it was on there). Unlocked ATT with T-Mobile.
The data worked just fine, I saw access point and didn't know if they moved it from the sim settings back to its own setting. When I saw tmobile was inactive, I simply touched it and from then on no data what so ever worked.
Soft reset didn't fix, restarting didn't fix it. What is happening is in cell+sim settings, the data connection is off and refuses to even move to the right, I can force slide it and hold it but then it goes right on back to the left. Airplane mode, not working. Wifi mode is on, connects, but no data is working. I can manually add an apn in there, and it says active but again no toggles work for data. As a result not a single app works except like call+sms. Other than that, I cannot do anything else (that requires data).
Resetting now, lets see how it goes.