I think you can utilize a Telguard configuration.
Not sure if you can pop a regular SIM card in though and the system appears to be tied in to a monthly account through Telguard.
Personally here I am done with AT&T and Verizon for anything related to cellular phones or internet connectivity or TV stuff or telephone stuff.
I had AT&T grandfathered services for unlimited mobile internet on a few accounts and they slammed me last year. I was was told that an internal memo did circulate to a number of vendors to get rid of the grandfathered accounts. I had multiple accounts with them since the 1990's.
When I first moved here I needed to get on line and used a modem. AT&T charged me (hundreds of dollars) for modem data usage (idiots that they were) such that I switched providers and never went back to them for copper telephone use. I wrote them off back then for copper use and recently for cellular use and now they are on my s-list.
I utilize Verizon for FIOS / Telephone service. They have slammed my account some 4 times now in the last 2 years. Each time it has been harder to fix. I am also done with them and they also are on my s-list these days.