The incredible hacker Core, has published a preliminary version of a client P2P for the iPhone (although if seems no credible), which is called Transmission Peer-to-Peer client for iPhone. But we must be aware that this is a preliminary version, and if you want to test it, you must take into account the following considerations: 

1. It’s unable to use the P2P application with EDGE, Wi-Fi only. In addition imagine with EDGE, how long to download… zzzZZZZ
2. For the moment this is a P2P client command line (without graphical interface) and thus will not be listed on the applications.
3. Using this P2P client will make the iPhone battery faster what sings a rooster.

We hope that with time the application is maturing and in the short term we can have a torrent client 100% functional and user-friendly for non Geeks.