Apple Delivers iPhone

I was going to get the treo 680 but forget it, im going with the iphone. Now I have very good wired headphones and also a very good wired headset. I really could care less about bluetooth headset, the quality I have experienced isnt that great. I would rather just hook up my iphone with wires. My question is with standard "headphone" on the iphone(3.5mm), is it possible for my 2.5mm headset to be connected to it. I have seen adapters but im curious if my headsets mic would really work, or if i would only be able to hear the person, without the person hearing me. Anyone have any idea?