Buzzing when speaking on the phone; how do I replace the Mic?

I saw elsewhere that the buzzing I experience on my phone is likely caused by a bad mic. It's great to have a diagnosis, but now I need to know how to replace a mic, or if it's even possible for a total amature to do alone. Is this the sort of thing I can try myself or should I try to find a service locally that will do it? My phone is about 2 years old so I doubt AT&T will fix it.
Thanks for any help!