External Microphone in Headphone Jack?
I found this video on YouTube: Galaxy Samsung S4 External Mic for mobile phone.  and here is the mic quoted on eBay. I plan to test it soon. It seems the vendor has positive feedback.

It is noise-reducing microphone for the 3.5mm jack. I tried to check if the cited video has stereo sound. I believe it does, but I am not sure it did not come from some YouTube stereo enhancement, so I cannot claim it for the microphone. I plan to use it for lectures, so it should serve for the purpose well enough.