I got a myself the Klipsch IEM headset. Looked like a good option for something with an inline mic, and the fact that it's based on something as well known as the S4 could make it useful to have as a reference in discussion.
 
But it seems I might be having trouble with it when I connect it directly to my mobile: When the remote button is held down the sound is clear, when it's released the sound gets muffled. Sounds like some sort of ground issue to me.
 
Audio works fine when I connect it with the Y-adapter which bypasses the input ring on the TRRS plug.
 
So, did I get a bad one, or is there some PC-input related reason for wiring a "gaming" headset differently than a regular mobile headset? (I don't have any front audio jacks on the old box I'm currently at, so I haven't actually tried it as a PC headset yet).

Got the idea to try my stock Sony Ericsson handsfree with the Klipsch adapter, and that caused the same behavior. So, I guess the conclusion is different ground/mic pinouts.
 
I think I'm starting to recall something relating to Nokia smartphones and pins. Might be an adapter to had.

I've now learned that it's my phone that's wired backwards (mea culpa), along with lots of other Sony Ericsson, Nokia and Samsung models (as explained and solved by, for example, Meelec).
 
Or, rather, most manufacturers now go with a reversed mic/common TRRS-wiring, which makes more sense since it makes it more likely that you can plug the handsfree into a regular TRS jack without accidentally grounding the mic.

I would just like to inform anyone with an Samsung Epic 4G (A Galaxy S phone), that it works perfectly fine stock despite the website the above user details listing the Galaxy S phone as one with reversed connections. I can say that it does not require the extra adapter for these IEMs.