Some questions about unlocking - which carriers can it work on

[Benz145]

Hey guys, some assistance would be much appreciated.

I have an iPhone 3G bought from AT&T. I want to sell it to a friend who lives in Finland and wants to use the phone to get 3G data from his carrier, Saunalahti.

Is it possible for him to do an unlock so that he can put his SIM in the iPhone 3G and get 3G data from his carrier? I understand that certain baseband versions are not compatible with an unlock; can anyone explain exactly what the phone would need to be able to do an unlock? It's currently using 3.0 software.

Thanks for the help!

[Simtech]

The 3G band is for US only I think.