Thought I would write a quick guide about pairing a Bluetooth headset with a mobile phone. In my case I used the M2500 by Playtronics.
1. On your mobile phone enable Bluetooth.
2. Turn on your Bluetooth headset. In my case press and hold the button at the back of the headset (but that covers the ear) for five seconds. A light will go green.
3. Put the headset into pair mode. In my case push the button at the back of the headset upwards and at the same time hold the button at the front down. Do this until a red light flashes.
4. On the mobile phone search for Bluetooth devices.
5. When it sees the device, select pair (or connect). I had to type in a four digit code, which on the M2500 is 0000 by default.
When I received and made calls it automatically used the headset.