Whew ! ...thanks for that Buddy.
Anyway, just in case anyone's interested, I've dug further and found out that the 4 contacts jacks are meant for smartphones and if you plug them into dedicated MP3 players, you'll only get sound coming out of one side, if you keep the button on the mic depressed they will behave like 3 contacts jack.
On the other hand, plugging a 3 contacts jack into a smartphone will do one of 2 things:
1) With Android phones, you get a weird sounding earphone or messed up controls i.e: tracks skips by themself or phone enter into call mode, on some models, you got both problems.
2) With Iphones, both 3 and 4 contacts jacks works perfectly if the phone is on before you plug in the jack, it seem the Iphone is able to detect which connector is plug in.
Looks like I'm stuck with having to burn in the FR201s on my HTC !