If you have a Motorola V600, you can control whether or not the phone automatically pairs with another device via the settings in the phone.

On my Motorola V600, there are various settings for each paired Bluetooth device. One of the settings is whether or not you want the phone to automatically search and connect to that particular Bluetooth device. If you select "no" on that setting, then the phone won't look for the X5 automatically. You would select "yes" for your handsfree earbud and "no" for the BMW.