Original post by: Josh Calvetti ,
Hmm, good question. The teardown that iFixit [http://www.ifixit.com/Teardown/iPhone-3GS-Teardown/817/2|performed] last year didn't indicate any differences other than capacity, but I'm not sure. I can't see why it wouldn't work, other than Apple moving connectors a bit. It looks like the exact same battery form factor.