Michael did a quick 7 minute and 22 seconds(!) video on checking your balance and remaining minutes using the GSM intercom. This also applies to the dialer and gate opener systems. It’s pretty thorough so all you need to know is there.
You can also use the forwarding to get info from your network; useful for setting up online accounts. Most networks send you a code to verify your credentials when you register a SIM online. You can use the FORWARD ENABLE command to get this information to your phone without having to remove the SIM from the door entry system or dialer.