I have found it really strange that everyone's talking about how iMessage works without talking about this... how does it really work? Forgive me if I'm missing the obvious, but I'm very curious about what's going on here. Before iOS 5: your phone sends an SMS to its carrier, it goes through the carrier's network, and then on to another carrier, etc. Now with iMessage: uh.... not sure. Here's MY theory, just to get the ball rolling (seems to be an absence of these theories on the web): when you sign in on iTunes and sync with your iPhone, OR sign in on your iPhone with your apple id, OR sign in within your Apple ID in your iPhone in Message settings, your iPhone connects with Apple Servers to say "Yes, this email (from your Apple ID) is now flagged as iMessage ABLE" *Conversely, or concurrently, when you send, or begin to send, a Message to a contact in your phone book: -your iPhone sends all the contact details associated with that contact card (the card in your local Contacts) to Apple -if there is an email address in that card (your local card) that is flagged as iMessage ABLE (on Apple's servers as above): -then it sends an iMessage. Otherwise, it goes through the phone network. Anyone got any thoughts, feedback, queries on this? Trying to get the ball rolling so we can all figure out what the hell's going on... Initially a bit confusing, though, isn't it! Cheers!