1.Building an android app that sends and receives messages and a server that checks the status of everything and reports it. Problem: Eventually the batteries expand on the phones and I cant find any modern phones that can run w/o a battery

2. Using https://smseagle.eu/store/en/devices/28-smseagle-nxs-9700-4g.html. Problem: The product is awful and support is worse. They use https://github.com/gammu/gammu which no longer has a maintainer so they sorta kinda maintain it. I don't have the resources to volunteer to be the maintainer and put it on my own hardware.

3. Use twillio. Problem: Not only is this expensive, but it doesn't test what I really want. I want to test sending and receiving from the actual telecom biggies.

Any suggestions? I am getting desperate enough to consider soldering something into a phone to trick it that it has a battery and want to know if there is a better way before I dig that deep.