The app that enables it is only available for jailbroken devices in the Cydia store for $5. The app is called BTstack Keyboard and is supported on iPhone 3GS
Engadget had a quick hands-on the application. Pairing your iPhone and keyboard was as easy as it could be. Works well over all the applications, though, cut, copy, paste is yet to get shortcuts. We can hope for more in future app updates, for the meantime it serves the purpose well.