Ok, heres an elaborate way to do it.
1.) Get a phone...
2.) Crack it open...
3.) Get a cheep mic from somewhere...
4.) Rip it apart and get the mic out...
4.) Place inside earpiece with mic faceing earpiece...
5.) Place ear piece back in snuggly, you my have to carve out a nich for the wire to run out of the handsets caseing...
Finnished? Awesome. You might want to get a soldering iron, the wires on my mic tend to come loose sometimes.