Apple iOS 6 firmware comes up with Facebook integration which can automagically update photos and user names for all matching contacts.
There is also one hidden feature that by using only phone number you can get any person’s Facebook user name and photo.
According to Techcrunch:
This started yesterday because a friend of mine tried setting me up on a blind date. He sent me a girl’s phone number and I registered it into my phone and just started chatting with her. I only had her name and phone number. Then I Updated All Contacts with iOS 6 and boom I all of a sudden had her full name in the form of her Facebook user name and her photo.
Now you can find any person’s profile on Facebook if you have contact number. So if you don’t have any information about a particular person and only have his/her phone number, you can easily get his/her Facebook profile picture to appear on your iPhone even if you’re not friends with his/her on Facebook.