If you are asking about the names of their incoming and outgoing mail servers, I don't know the answer, but I do know that you can set up Hotmail on your iPhone in the ordinary way you set up any other POP3 account. The iPhone seems to know the names of the correct POP and SMTP servers.
I've done this in the recent past and it does work. It didn't used to.
Edit: I just set up iPhone Mail for my Hotmail account again. The incoming server (POP3) name is pop3.live.com. The outgoing server (SMTP) is smtp.live.com. But as I said above, you don't need to know this to set up Hotmail on your iPhone.