Apple introduced some pretty significant integration with Twitter in the last iOS update, and there’s a few nifty things you can do with it.
One of the new features is the ability to use Twitter to match up usernames and photos with the contacts in your iOS contact book.
To do that, head to the Settings app, then select Twitter down the list. Once in the Twitter page, you should be able to press “Update Contacts”.
There, Twitter will do all the work and update your contacts list with that new information.