AT&T "mobile network disconnected" error in new HTC U Ultra phone
I set up a new HTC U Ultra phone a week ago and everything was fine, but a few days ago my mobile data stopped working. Data roaming is turned on. I've checked the APN settings and they seem correct. When I try to view network preferences, I get a "Please make sure you have valid SIM card" error message. I have a valid AT&T SIM card.
My previous phone was also an HTC U Ultra and I had no problem with mobile data with that phone.