Lecture 12 from the Stanford University iPhone Application Programming class was hosted by Alex Aybes. Alex covered using the address book functionality provided in the iPhone SDK.
His talk included several demonstrations of the C-based Address Book API, along with some of the ins and outs of Core Foundation, which shares many of the same concepts of the Objective-C based Foundation framework. His demos showed how to use the various person view controllers, getting person entries from the user’s Contacts applications, and diving into these entries to read and update the values existing in the person entry.
This does not directly apply to any of the applications I am currently working on, but no doubt it eventually will be useful in my development efforts. If you have a need to access the address book entries in the iPhone Contacts application, this is the presentation you want to check out.