Apple has gone live with a Game Center page on its website and it's bad news for iPhone 3G users hoping that they would be able to come and play - you're not included.
Game Center will work (after an iOS 4.1 upgrade) on iPod touches from the second generation onwards as well as iPhone 3GSs and iPhone 4s.
It was thought that the second gen iPhone touch would miss out (it shares a lot of hardware specs with the iPhone 3G) but Apple has included it in the official lineup.
"Game Center lets friends - and soon-to-be-friends - in on the action. Invite someone to join, then get a game going. Or go up against people you don’t know, from anywhere in the world, in a multiplayer game. It’s your world. Everyone else is just playing in it."
The Game Center app should appear after the iOS 4.1 update (which is due anytime soon), and you'll be able to log in with your Apple ID. You'll stay logged in for good, or, until you decide to leave.