That's just the typical Bittorrent /client/, but the idea of using Bittorrent means the /protocol/. A special Bittorrent client could be written for ISPs with uploads disabled and Apple could also disable them on the update-downloading Bittorrent client for the phones.
The clients (be it Bittorrent or not) would still download the MD5 hash after the download finishes to verify the integrity of the download, and Apple would still be able to measure the amount of downloaded images.
So then all the networks that have done $things to BitTorrent to demote it to second-rate traffic will suddenly have a bunch of very angry Apple fans whose downloads are mysteriously having issues. And then - assuming you intend for more things than just Apple to go this route - all the CDN's would need to be redesigned to support BT too. It seems like it'd be simpler for Apple to figure out how to validate a partial download and then resume. It isn't like that would be cutting edge technology. I think I might even have seen it happen before. ... JG -- Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net "We call it the 'one bite at the apple' rule. Give me one chance [and] then I won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN) With 24 million small businesses in the US alone, that's way too many apples.