This is a difficult repair, unless you are skilled in SMD re-work. Water damage is a common cause for the Mic going bad, so often times an ultrasonic bath will do the trick. If your microphone does not work I assure you that the majority of repair shops in the United States are not this skilled. Just check out their site over at celmetro.com and you can see that they really mean business. Talk about professional! Compare that to the fly-by-night, sandal wearing, consumer crazed techs that exist in America…well you get the point. That is not to say that people in the States don’t have these skills, just that you should ask around to be sure.
One time I screwed up an iPod Touch 4G repair. The fix required micro-soldering so instead of experimenting on someones device, I called around and found a services that assured me they were skilled at this and had done it several times (I later learned to do it myself). Long story short, they completely screwed it up, much worse than before. I was shocked and after that day decided that if something was to be done correctly, I’d have to figure it out myself.
This may be the most badass repair shop I’ve ever seen.