I just tried turning the phone radio off and in Garmin Mobile XT, it got a GPS fix no problem. Don't see why the GPS would work only with the phone radio on. Are you putting it into flight mode instead of just turning the phone radio off? Flight mode probably would disable GPS as well. I don't use TomTom so I can't you out with that program in particular but I can tell you that the GPS does work without the phone radio.
