I've posted this problem before, in another post. Just posting here too, simply to join the club. Same mic issue for me. Others cannot hear me well while I can here them crystal clear.
P.S. I replaced my first X5 device within 4 days from purchasing it and apparently the problem exists in my current (2nd) device too. I didn't replace the 2nd one because the mic issue appeared after "root". That's weird...
P.S. 2 I really love this phone. It's a high end device in an extremely affordable price and I DO NOT WANT to replace the specific model whatsoever. However, this has been a very frustrating thing and still no one has come up with a solution!