3gs 16 into a 3gs 8 case what problems should I look for?

[brainzbody]

I have a16GB 3Gs Basically works except the earbuds seem to not work (yes I have tried cleaning)
The volume bar fell off. I have a new 3Gs 8gb. So I know the flash is soldered on the motherboard, so it makes sense to me to open both phones and swap the motherboards.
This would give me new battery, new screen, new volume bar and new earbud plug.
I assume the motherboard is what is actually registered with AT&T. Are there any things I should be looking for?
I have too much data on my 16 to fit it on the 8GB

any sage advice?
Iuse PDAnet to tether since I live in a small black hole with zero internet.

[Cowboy]

No you should be good

[Kenneths]

iphone's capacity is always satisfied users. But you said I have not seen.