You shouldn't need to disable ActiveSync, the Pocket PC will change its device type as soon as you start th WMODEM program and type the [START].
However I had this problem last year, and it solved by itself. At that time I pointed this to authentication.
Yesterday (25 May) I couldn't connect the Apache to the data stream while in the Auckland airport on my way to Singapore. Perhaps, what Jama doesn't know, is that there was an authentication outage these days? Perhaps related to the Xtra authentication problems?
There is no link between Jamamobile and Xtra from an authentication perspective. CDMA uses a different RADIUS to Xtra. The common part is that Jamamobile does backhaul through Xtra for internet. So, in that perspective Jamamobile is a big fat Xtra customer.