iPhone OS 4.0 Beta is already leaked and in order to get it installed on your device, you need an Apple Developer account. There's a catch though. You can't simply sign up the developer account; you are required to pay USD 99. I don't think it's worth to pay that much for the sake of trying iPhone OS 4.0 Beta which will eventually come out around this summer. Fortunately, there is away to get around this problem (install iPhone 4.0 beta without UDID registration), thanks to ih8sn0w.
