I don't have a PDA that has USB and this limitation is really hurting me when it comes to more "mobile" devices built with Phidgets. I say WIFI, Bluetooth whatever. please don't make me beg!
Wifi would be cool, but even now ad-hoc networks just don't seem to work well, so you'd probably need an existing wireless network framework. On the Phidgets side - Wifi is very complicated and expensive to implement, and sourcing wifi chips at low volume is very difficult.
Bluetooth would also be cool, and I think it makes some sense to create a bluetooth adapter board that would allow any Phidget to be converted into a bluetooth enabled phidget - I can't see us producing dedicated bluetooth phidgets.
Both of these ideas have been discussed, but we just don't have the resources for pursuing them right now.