I created a barebones driver for T-Mobile Home Internet's gateway.
The only functionality it supports right now is rebooting the gateway, and the only model supported is the Nokia version. This is basically what I needed for my own purpose.
I'm sharing it here in case somebody else finds a use for it:
The logic is that of highvolt-dev's tmo-monitor, adapted for Hubitat.
Feel free to log issues in GitHub or contribute if you would like to enhance it.