How do I fix "could not activate cellular data network" problem when returning to US after traveling and using a different SIM card? After traveling overseas (Vietnam &amp; Japan) and using a SIM card for each country, I restored my AT&amp;T SIM card into my iPhone and got:



I tried the suggestions in https://support.apple.com/en-us/HT201415 and all of the suggestions in https://appletoolbox.com/2013/04/iphone-could-not-activate-cellular-data-network-fix/ except backing up and restoring, but nothing worked.
I called AT&amp;T and was asked to see if there is a profile at the bottom of Settings->General. There was, and deleting it fixed the problem. Apparently profiles are often installed when using overseas SIM cards.