They are pretty much same sounding. The different in sound for old and new MH1(including MH1C) is a result of different filter material, and has nothing to do with whether it is a MH1 or MH1C - and the only way to know what kind if filter is used is to buy a pair and look at the filter yourself. However, as far as I know, the difference between the different filter is not that big.
It is either a Sony Ericsson green logo for MH1, or an engraved 'SONY' marking for MH1C. Which is it?
Anyway, as I have said before. iPhone use a tiny chip in the remote to detect whether it is a made-fo-iPhone headset or not. MH1 (or MH1C) doesn't have that chip inside so it doesn't detect automatically. You can try to press (hold down) the center button on the remote when plugging the headset it and see if it will detect it or not. Even if it detect the remote, only the mic and center button will work, volume buttons won't (again, it is because of the chip iPhone required).
Err, not true at all.
Oh? did i get that wrong? my bad