If you want to pair Bluetooth headset with or any other Bluetooth accessory like Speakers, car kits here is the guide to Pair Bluetooth device with Windows Phone 7 mobile.
Pair Bluetooth Headset with Windows Phone 7 Mobile
Step-1
Tap “Arrow” on Start screen or Slide to left on Window Phone 7 mobile.
Step-2
Tap “Settings” then “Bluetooth” menu.
Turn the Bluetooth status On by tapping on On/Off Button.
This will start searching for Bluetooth devices (Make sure your Bluetooth headset is Turned On and discoverable).
Step-3
Tap the Bluetooth device that you want to pair with Windows Phone (If you need to enter a PIN to pair, use the same PIN on both devices your Phone and Bluetooth headset).
Unpair Bluetooth headset Windows Phone 7 Mobile
Tap and hold the name of Bluetooth headset in Bluetooth settings and then tap “Delete”