[4sound]

The Shure MPA-3c has a 3.5mm jack with a build in mic so you can plug your own headphones in and use it with your iPhone. 
 
I've rewired a few headphones to be short (below the chin with a 3.5mm plug) so I can plug in the Mic adaptor to my iPhone.  I've tried all of the other mic adaptors out there and the Shure MPA-3c was the best by far.  (Griffin makes one that's ok) Doing a search to buy another one and they're no where to be found???
 
Anyone help me find a source? Or know any other options out there?
 

 

[zzffnn]

I have the same idea like yours and did a quick research. This one may work but I do not know about its quality:
http://www.amazon.com/Headset-Adapter-Microphone-iTouch-iPhone/dp/B002ZX695U/ref=pd_sim_e_1
 
It does not look a lot worse than my iPhone 3GS' included earphone with mic, at least.