Welcome to the forums colinb43. The instructions for pairing the Plantronics Voyager 510 and 520 models are the same;
1.) Put your phone into pairing mode
This can usually be accomplished by going under settings in your menu and selecting Bluetooth. Follow the prompts to "find a new device." If you are having problems, refer to your phone's user guide.
2.) Put your Voyager headset into pairing mode
Start with your headset on. Press and hold both the call answer button and the volume up button (marked with +) until the indicator flashes red and blue.
3.) Select the headset in your phone's Bluetooth device menu and enter in universal key
Your phone may or may not ask you to enter in a key code. If it does, the code is always four zeros: 0000
4.) You are paired up!
They are not much different for the VoyagerPRO;
1 Turn on your phone