Seems like I won the unlucky lottery and loaded up Touch days after "support" for Volte broke. I have a Pinephone Pro that works but is in a VERY early state of development, and everything but the phone works on the Pixel, so I have two paths to follow as this evolves. That is the price you pay for getting in early, I was just surprised because EVERYTHING indicated it worked, which was true until just now.

The Pixel 3a XL is listed as being supported in AT&T's new network config. My carrier (Patriot Mobile, using AT&T) ran the IMEI when I ordered the SIM/service and nothing flagged for them. Perhaps it works only with VoLTE (not yet on Ubuntu? mandatory for AT&T calls?) which your second link suggests? It is all clear as mud, but if thats the case seems like its a paperweight. Which begs the questions, what phone DOES work with Touch and AT&T? And if the answer is none, what carrier works with Touch on a Pixel? Unfortunately AT&T is what the repeaters are at work, so I almost have to stay with them or have no coverage 12 hours a day.

I tried switching network types and selecting anything other than the 4G option shows no network, expected. Also, all the call forwarding options are checked and cannot be unchecked and the number forwarded to is AT&T voicemail.

I am by no means savvy on phone tech, it was one of the things I was content to just go consumer on but that is less and less acceptable and I want to make the move to linux. So far I have an unshipped Librem 5 (Pursim is super scummy), this Pixel 3a which it seems lost viability a week before I loaded Touch, and a Pinephone Explorer which is far from viable software because it was just born.

@subarubrat I could not edit the post, so an update.... I found that cell data is now working, not sure what step resolved it but that is fine. So the only thing not working now is the inability to make or receive calls. It just displays "Call Failed" then returns to the phone app dial pad.

So far: Bought a new SIM through AT&T and got the text message it is activated. The phone is a Pixel 3A XL with a fresh Ubuntu Touch install. It seems to work perfectly in all respects other than:
I can send/get texts with other phones normally.
I cannot make or get calls, trying to place a call results in "No Calls" or "Call Failed" being displayed.
Cellular data does not work.
Under Settings/Cellular it shows no SIM if the SIM is out, and with the SIM installed I get
Carrier and APN populated as AT&T, connection type options are populated, and under
network it shows AT&T with a full signal triangle with an L in a white box next to it.
The SIM has no PIN set, when placed in an iPhone it makes and gets calls normally. My SIM from the iPhone gets the same results of no calls/data when placed in the Ubuntu phone.

As far as I can tell, I have two perfectly fine SIMs that work in my iphone, when either SIM is installed into the Ubuntu phone it is recognized and everything seems normal other than calls/cell data not working.

I did a wipe and new setup on the Ubuntu phone and the same results occurred. I am a 25+ year Linux user but this is my first experience with moving to a Linux phone so I am loving this but I have to confess I am out of ideas here.