Address Book you can read/write fairly easily and powerfully as it has many commands such as ABAddressBookAddRecord, ABAddressBookSave, etc.
Pictures, last I checked, you can't replace, but you can definitely grab a picture from the photo picker, then modify it, then save it back to the Photos app as a new picture using UIImageWriteToSavedPhotosAlbum.
Videos work the same way as Pictures using the UISaveVideoAtPathToSavedPhotosAlbum in the 3.1 SDK.
what about call logs
voicemails(i am sure they wont allow us to touch that)
to-do and notes ( apple wont allow us to touch them either)
ringtones ( apple wont allow us to touch them either)