My iPhone XS AT&T (iOS 17.3.1) stopped making and receiving calls

I was not getting calls or able to call out. My screen shows "Call Failed" and then at the bottom the X for cancel and the green phone icon for Call Back (didn't work obviously). I have checked every setting on the phone - - I had not changed anything

• My spouse is on the same account and his works
• I checked my settings to his and can't see any differences.
• AT&T Account, but since his works it seems odd that it could be another outage.
• I keep the iOS current - auto updates on.

solved: Power OFF then ON again. But anyone know WHY this happened? This is the second time - and the last time there was a minor emergency and I had to borrow someone else's phone.