If you're new to us, you should check that your contacts are saved on your old phone and not the SIM as your SIM may not be compatible with your new Three phone.
Then to transfer your contacts:
On the homescreen, tap All apps
You'll see a message, tap Next
Choose the make of your old phone, tap Next
Choose the model of your old phone. If it isn't there, tap Others followed by Next
Turn on Bluetooth on your old phone, tap Next
Once your new phone has finished scanning, tap the name of your old phone. Tap Next
To connect your two phones, you may need to confirm that the passkey matches the one on your old phone. If it does, select Accept on your old phone
You'll see your contacts on your new phone, check the box and tap Next
Tap Accept if your old phone asks you to authorise the connection. Your contacts will transfer, tap Done
Your contacts will now have been transferred to your phone.
Note: If you're upgrading your phone you should make sure that your contacts are saved to your existing SIM. To find out how to do this, check your old phone's user guide. Once your contacts are saved to your SIM, just insert the SIM into your new phone and it'll automatically read the contact information.