Will iPhone 3GS work on a 3G?

[iPhone3GS]

So I was on amazon.com and bought an iPhone white back housing, and ordered it (my iPhone 3Gs is very screwed up on the outside) bow that 1 day ha passed by I checked my order information and it said it was for an iPhone 3G and now I can not cancel my order (*facepalm*) so since iPhone 3Gs and iPhone 3G are the same thing on the outside I was wandering if it will fit in the back housing. Please leave your opinions and ideas. Thanks

Like-A-Boss