All credit goes to rcadden a member on MoDaCo for pointing this one out!
You can manually match up your Facebook contacts with your phone contacts. To do this, first make sure that in your Contacts app, you press menu, view options, and choose to display your Facebook contacts.
Now, go through your contacts list and find whoever you need to match – press menu, edit contact, and then press menu again, and choose ‘Join’. Now you can find their Facebook entry and manually match them up. I had to do this for a few of my contacts where I have them stored under a different name from their Facebook profile.