http://discussions.apple.com/message.jspa?messageID=6924615#6924615
ATT was quite specific that *82 is the ONLY official way to selectively block a caller ID. While the GSM code may work for whatever reason with the iPhone and possibly on international systems where *82 may not, if you want your domestic US Address Book to synchronize uniformly with *82, follow the procedures outlined in the other thread. It will certainly keep me from having to go in and manually change all the contacts with *82 to *31#