So this is where some things become a little unclear to me.  I'm using my own base with the VRS.  If I were to use a cellular modem that could plug into the USB port and provide internet what would I look for?

My TMX does not have a radio.  I removed it when I unlocked and installed the second GPS receiver for implement guidance.  I learned last summer that because of the I cannot configure it to accept serial NTRIP corrections so I had to unlock VRS to make it work.