After checking syncmyride.com for supported phones, make sure that you have the latest firmware installed on your phone.
My Blackberry 8900 works ok, but txt messaging read-back is not supported and incoming callers hear a short, high-pitched beep when I answer the phone. I've looked at this on other forums, and I believe it's due to my phone being down-rev'd with the firmware.
Another item on the to-do list!