If its the earpiece speaker why don't you just change the speakers around?

Put the broken one in the unbranded one in the AT&T and the working one in the AT&T in the unbranded one and then send the AT&T back as faulty. Just say you dropped the phone if they ask why its been opened.

you'd save a lot of work!! But then again i have a tendency for saying daft things when im busy. NO COMMENTS!!!!

Lav