I used to do the same thing long time ago w/ Sony DS220. But it only pair one device at a time (I have HTC Tytn II, Dell X51v, Asus P525) and doesn't have FF/RW. So, I just brought a JVC KD-BT1 which have buildin BT support w/ multiple device support. It's a much cleaner solution and auto re-connect to my device once I start my car.
My SE X1 rom-> http://forum.xda-developers.com/forumdisplay.php?f=471