I have Verizon Treo 650 with firmware 1.04. If you get any of the Treo 650 with the latest firmware (or upgrade the firmware through palm.com) you should have no problems with BT synching with your X5.

My X5 and M3 both pair with my Treo 650 Bluetooth.

Also, for synching and storing data, the Treo 650 Palm OS is tops. You should get Backup Buddy which can backup your data on your PC hard drive and also back up data on your SD card on the Treo 650 itself. However, the memory in the Treo 650 is better than previous Palm because even if you lose power, the data in the memory stays intact.

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