I use a Unifi gateway as my router with two sources of internet - AT&T fiber for regular internet, and a T-Mobile 5G cellular MVNO for backup internet (when fiber goes down). In both cases, the Unifi gateway is the router. No issues.
This is the backup internet MVNO that I use (thanks to @ogiewon for telling me about it). It is $13 a month when prepaid for a year.
Their SIM will work in any 5G modem.
I used my own access points I bought various models unlocked from eBay mr6500 mr5100 etc. the pool plan I use comes with 2 sim cards darkstar(att) and a Verizon one. u have your choice. can not answer other question as I only use for data no phone.
Good approach. I did that with my unifi gateway data a while back, and it gave a similar result.
Sure I used a bunch more during game or other large software distribution downloads, but all the rest of the time it was pretty low (50Mb or less for sure).
The one area that I do focus on is UPLOAD speed, as whenever I have to re-seed my offsite backups that would be hugely impacted by a reduction in upload speed.
If I ever had to disaster recovery from the cloud backup en masse that would be painful with a slower download speed, but that should be rare/if ever.
https://www.usmobile.com/help/docs/managing-lines/privacy-security#enhanced-security
There is also SSO, 2FA, and Passkeys if desired. https://www.usmobile.com/help/docs/managing-lines/privacy-security
Excellent, thanks very much for that information. I'm not sure why it didn't turn up in my searching clearly my Google Fu was not up to speed...
This is the real answer 
