I looked into this for my wife, who wanted something to sync with her Mac. The 755p can provide service to other bluetooth-enabled phones that support bluetooth DUN, I've done it on a WM phone (PPC6700) before. However, the iPhone does not support that profile, since presumably ATT made them leave it out. The iPhone and 755p do not support USB host mode so no USB solution could work.
If you can carry another bit of hardware, you can pick up a PPC6700 or newer with WmWiFiRouter, which should allow you to take the bluetooth DUN off the 755p (the 755 needs usbmodem) and the application lets you use the 6700 as a wifi access point.
My wife got an LG Lotus instead, BTW, and syncs with Google.
Other than that I think you will have to wait for a jailbreaker to port the bluetooth profile, as mentioned, but since the bluetooth in the 3gs is different than the older version it might never happen.
Good luck,
-TC