The release of a tool capable of unlocking first-generation iPhones for use on unofficial carriers as well as allowing full read/write access to the filesystem -- thereby enabling installation of unofficial, "jailbreak" applications -- is imminent.
The iPhone Dev team has posted a screenshot, seen below, of an iPhone running OS 2.0 with both the App Store (Apple's third-party application solution) and Installer.app (the unofficial third-party application solution) running side-by-side. The iPhone is also unlocked, per the MTS carrier logo -- MTS is an unsupported wireless carrier.
Another screenshot shows the tool "BootNeuter" loaded under iPhone OS 2.0. This utility allows users to fully unlock the iPhone for use on unauthorized carriers.