Microsoft took away ActiveSync over the network (wired and wireless) a few versions ago and did not give it back with Windows Mobile Device Center. But, the sometimes flaky USB connection is not your only alternative.
My K-JAM Pocket PC Phone Edition, for example, syncs on the first attempt over USB. But, it somehow corrupts ActiveSync on the desktop for subsequent syncs unless I reboot my PC (and, yes, I’ve tried terminating and restarting the ActiveSync service). None of my other Windows Mobile devices causes this problem. Just the K-JAM. My solution has been sync the K-JAM using Bluetooth exclusively. This does not corrupt ActiveSync for subsequent sync sessions. The only downside is that I need to initiate ActiveSync from the K-JAM.
The GeekZone has detailed information on setting this up….
Bluetooth ActiveSync Guide for Windows XP Service Pack 2
If you have ActiveSync Bluetooth issues, take a look at this Microsoft Bluetooth FAQ…
Frequently asked questions about Microsoft Bluetooth-enabled devices