This is a replacement for .Mac and now provides push of mail, contacts, and calendars to the iPhone.
When I first heard about MobileMe, I wondered if I’d be able to keep my mac.com email address. For the first couple of years of .Mac, it was pretty much the only reason I subscribed to .Mac. Later on, I did find the sync of calendars and address books to be pretty useful.
Apple answers the question of Mac.com email:
As a MobileMe subscriber, you can continue to use your mac.com address for email. You will also be issued a me.com address with the same user name that you can use if you prefer. The choice is yours.