AT&T logic board fit in sprint phone?

I can't think of any good reason why i wouldn't, generally they would follow the same layout as they use the same antennas. That being said, the logic board of a Canadian Galaxy S3 will not fit in an American S3.

I'd say it's safe to try, Just make sure the midframes on each one have the same grooves and slots. Make sure the batteries have the same voltages or switch them too