Had a Moto V551 on Cingular, which worked perfectly, but Cingular's GSM service in my area sucked. Got rid of it and moved to Sprint. My Sprint Treo 650 works great as well, but only the contacts stored in "favorites" will transfer to the X, which is o.k for me. Only other minor complaint with the 650 is that when the X initially connects with it, the 650 screen turns on, and it bypasses keygaurd. I wear the 650 on my belt, so when this happens, sometimes the seatbelt will push on a key and either launch an application, or dial a number. The solution for me is to take it off my belt, and put it in the cupholder tray while I'm driving.