The iPhone by Apple was introduced in January 2007 and as of 2009, it has taken 3rd place in the overall smart phone sales. In April 2010, over 50 million iPhones have been sold Worldwide. The increased use of the iPhone is seen in both business and personal use.
Apple is ever extending its iPhone operating system (iOS) onto their other devices including the iPad, iPod Touch and Apple TV.

A whole host of information can be recovered from these devices through various Digital Forensic Techniques.
These can include but are not limited to:

General device information and settings
Phone Information
Call Logs
Text Messages (SMS - Short Message Service)
Picture Messages (MMS - Multimedia Messaging Service)
Contacts with Photos
Custom phonebook field labels
Calendar
Notes
Tasks
Pictures & Images
Camera Recordings (Still & Video)
Audio Recordings
Music
Video
Email
Web History
Bookmarks
Cookies
YouTube
Internet Data
iOS Applications
Google Maps
Voicemail
Passwords
User Settings
User Property Lists
Speed Dials
GPS (Locations & Satellite Navigation)
File System Data
3rd party applications settings
Office Documents
WIFI
Paired Wi-Fi networks list with their geo position
Paired Bluetooth devices list
Skype calls, chats and SMS messages history
Skype address book
User dictionary