iPhone Dev team have posted in there blog that they have successfully downgraded iPhone 3G firmware to an older version…..

This image is the “About” screen from a 3G iPhone that was bought in a store last week. As you can see the modem firmware version has been successfully downgraded to an older “beta” firmware. This is not an unlock (yet), but it is our illustration of the first progress made with regard to hacking the 3G baseband. We have accomplished this by being able to execute our own code on the baseband that allows us to circumvent security checks and flash the baseband with older, disallowed firmware. Please note this has been accomplished using software only, the iPhone 3G has not been disassembled or hardware modified in any way.