This appears to be an AT&T provisioning issue.
I got to poking around around and found that they stuck the device under a NEW plan, with NO data. The usage tracker shows my test SMSs. No data at all explains the ‘no auth’ messages when I tried using PPP.
Old thread but I’d forgotten to share.
In the end, activation worked when we used a different device, and then sim swapped.
Since then it’s worked pretty well, with some interesting quirks now and then.
Great example - yesterday down in the florida keys, internet was being very, very slow. Via my phone as a hotspot on the same carrier, no problem. I finally just powered the pi down for the evening.
This morning, I powered it up and it worked great!
I’m suspecting that roaming across the US caused it to get kinda goofy - maybe a stuck ip tunnel or something, dunno.