ginge at present there is no way to unlock/change the imei# on the 3g and 3gs iphone. If it were a 1g or 2g version then yes there is a way to do it as it was software based then. in the 3g/s models it is actually another chip on the motherboard with no access onto it.
Your options are either to have a pretty paper weight or get hold of another motherboard in working order that has not been black listed.