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so can i read/write/modify the first 3

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.
 
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