Actually, I've experimented with the Apple headphones a lot...
I originally wanted to use the $80 Apple In-Ear headset because they fit my ears nicely. I got the same reaction as you did with your ear buds; that is, I could only hear through them, and not speak into the mic. This is the same case with the newer earbuds that come stock with the new iPhone 3GS's (with volume control).
I kept trying to find a solution and found that the original iPhone headset (one button ONLY) works great with the phone. After doing some research I found that the problem was the it had to do with the 4-pin layout in the newer headsets that conflict with our phones.
So, I'm stuck with a headset that works great, but just doesn't fit in my ear too well... oh well, I'm probably going to end up swapping the Apple buds (the drivers) with some in-ears by soldering them on.
Good luck!
