Friend of mine who bought iPhone 3G spilled a coffee, I mean alot of coffee,

that couldn't get a warranty due to liquid damage, so she had to buy a new one. She game me the broken one to do whatever, so I tried to sell the parts but unsuccessful due to liquid damage. (corroded inside).
Now I am thinking, would it be possible to swap the 3G case to my 2G iPhone. I don't want to pay for 3G service, but like the case......
Do you think it is possible? I don't want to do this myself, and would appreciate any advice if you know who does this.
Thanks in advance.