I posted an issue in another thread about PDANet not working, which is somewhat related.

It appears that anytime ActiveSync becomes active, it disables my ability to use the internal modem on the device. When I plug the phone into the USB cable, the Treo drops the EVDO/1x connection. When I try to reconnect to the net, it tells me that the modem is in use.

Anyone else have this issue? It just started happening.