There's bad news for those of you with old iPhones. Apple has confirmed that the latest beta of Game Center is a no-go for anything older than an iPhone 4. That means that iPhone 3Gs and second generation iPod touches are out for Apple's social gaming app. It's probably for the best; you've likely already heard about all of the issues that 3G iPhones are having with iOS 4.0, and freeing itself from the requirements of the older hardware means that Apple should be able to make Game Center as good as it can be.
But if you have an iPhone 3G and were looking forward to trying the new app from Apple, you'll have to change plans. Either go grab yourself an iPhone 4 (which is what I'm still planning to do -- my original iPhone is looking super old at this point), or stick with the social gaming networks that you've already got access to.