(From public article)

Changing APN for T-Mobile and multi-carrier SIMs such as Twilio, Teal, Hologram, etc.

Note: Changing APN for AT&T and Verizon requires additional steps. See instructions at bottom of this page.

Step 1

• Connect gateway to ethernet.

• Locate the gateway’s IP address (you can use an IP scanner).

• Get gateway’s password, which is the serial number on the sticker on the bottom of the gateway.

• SSH into gateway using a command line interface program like Terminal on Mac or Command Prompt on PC:
  ssh root@192.168.2.xxx

• Password is the gateway serial number.

• Enter following commands to check the system version, current firmware, and current APN:

...

/opt/Sierra/LteModemFW/lte-fw-download-script.sh att /dev/shm/

Step 4

• Connect gateway to ethernet.

• Locate the gateway’s IP address (you can use an IP scanner).

• Get gateway’s password, which is the serial number on the sticker on the bottom of the gateway.

• SSH into gateway using a command line interface program like Terminal on Mac or Command Prompt on PC:
  ssh root@192.168.2.xxx

• Password is the gateway serial number.

• Enter following commands to check the system version, current firmware, and current APN:

system_version
konaLTEmodem.py -c "at!gobiimpref?"
konaLTEmodem.py -c "AT+CGDCONT?"

Output will look like this:

...