Implement add contact as in iPhone SMS app

I want to build the 'add user' functionality as it is available in the the messages app, where when the user starts typing a username the app searches for the appropiate user and shows it in a circle as in the screenshot below.

It this a build in functionality? If so, what is it called? I would also like to know how to implement the bar which contains the user names, especially the fact that when editing the bar autosizes to show all the users (in case of an sms being sent to multiple recipients) and when the focus is off the bar it just shows: 'To: John 开发者_如何转开发Doe, recipient 2 and 5 more'

Thanks in advance for any help!

P.S. can't include the screenshot as an image because i'm a new user but here's the url: Compose SMS view

Take a look at the Three20 library in particular the TTMessageController and/or TTPickerTextField classes.