Weird that DataMonitor wouldn't work when the phone is in tethering mode. Not to split hairs, but cellular modems don't work like dial-up modems anymore. The type of "dial-up" connection that cellular devices used to be able to initiate (CSD), are no longer supported by the wireless carriers (at least not in normal circumstances). The wireless connection on your BlackBerry is just like any other wireless session, with the exception that the phone is relaying data to an external device.