Both of those questions get answered in the following two videos. First is the one about the other carriers, then the one about hacking/unlocking.
In this first video Steve makes an analogy about Apple choosing O2 over the other carriers, he says its like going on a few dates before you get married. Pretty good analogy if you ask me.
This second video answers a question about Unlocking and hacking. Steve says it’s a lot like a game of cat and mouse.