Just found another seller on ebay that has this:
Cell Phone 2.5mm Microphone MP3 Stereo earphone adapter
Most cell phones with a 2.5mm round plug for earphones have 4 conductors. (Microphone, Left, Right and Ground)
This adapter has the 4 coductors on the 2.5mm plug end, and a 3.5mm socket with standard 3-conductor Stereo output.
(The tip of the 2.5mm plug is the microphone)
So this could be another choice. Price is $10 vs $5 for both above, but this one has the mike, volume control and answer/end button.
Anyway, if microphone is the tip, then this could also work.