I'm no genius, but as far as I know any modem functionality is not enabled/disabled through BES. I've set up two devices as modems; 1) A 7130e that tethered without any additional software, but needed a plan from the carrier and 2) A 7520 using a 3rd party app called Shark Modem. With neither of these did I need to do anything in the BES.
The 7130 solution worked much better, but neither was fantastic. I'm curious, what requires you to set up a device as a modem?