Or have a centralized server, a la Xbox Live, Battle.net, etc. If users of the game "sign in" to the server, than anyone can connect to anyone. Plus, your pho

Or have a centralized server, a la Xbox Live, Battle.net, etc. If users of the game "sign in" to the server, than anyone can connect to anyone. Plus, your phone's contacts typically have iChat contacts associated with them, so if done well, the system could match up based on phone number and/or ichat screen name, and be able to find mobile and desktop clients of your friends.