Phone compatibility question

The manufacturer must submit the phone for certification testing. How exactly that is done, I don’t know, but it’s not done through this forum.

This statement from them will tell you it won't work on ATT as they are not certifying with US carriers.

Sandblaster - thanks for the reply, and I realize these forums are probably not the best place for trying to get a phone approved, but in the world of AT&T, it's almost impossible to navigate to the right support department. My hope was to get someone who works for AT&T, reads these forums & has a connection to the engineering department. I have dealt with another carrier in the past with a similar issue of the phone (Moto X Pure) not being on their allowed/approved list. In that case the phone had not been submitted for certification because the carrier was not going to offer it in their lineup of phones. However I was able to have a request sent to the engineering department, they allowed the activation with the caveat that the carrier would not guarantee the data reliability or functionality until full compliance testing was completed, which began when my request for activation was submitted (eventually the phone was added to their approved list). 

Glimmerman76 - Your reply doesn't change my hope for a solution. The Ulefone seems (technologically) compatible with all US carriers (using LTE) except for those carriers that choose to utilize a whitelist that doesn't seem to be based on any technological compatibility, but instead based upon "manufacturer didn't submit for certification" premise. Those days of GSM vs CDMA are thankfully in the past, so now reliability for voice/data is based more on whether the device's radio has the capability of utilizing all the frequency bands that the carrier uses to provide coverage. Seems to me that a company in a competitive market would be slightly more flexible, given how these days with all the specialized features that some of these devices are capable of, and that some end users have the need for. In my case, the CAT S62 Pro has some of the features I want/need and is on AT&T's approved list, but technologically the phone is 2+ years overdue for an upgrade (new model due 4th quarter of 2023). Is it so terrible to instead be wanting to purchase a phone that has the features I care about along with the latest processor, latest Android OS, superior camera & a headphone jack? I know - the common attitude of "well, just switch carriers" is less than helpful & unfortunately not an option at this time. Again I hold out hope for an AT&T employee to chime in and offer to find a solution - instead of the all to common these days - "sorry, it's just the way it is". 

I have experience with trying to get phones on the whitelist.  It's not just that easy.  The carrier needs to be sent phones from the OEM.  It took Sony 4 years to get it done on Att.