It would be nice to have a well made adapter that would allow many of the current cell phone headsets to attach to the KX3's Mic and Phones jacks. These headsets span the range from the $300 Bose QC-15 noise cancelling headset to the $20 Apple iPhone earbuds.
These headsets all share a common interface where both the mic and the stereo earphone connections are brought out on a TRRS 1/8" plug. An adapter that would accept the TRRS plug from the headset and split it out to properly wired right angle 1/8" plugs to connect to the KX3's Mic and Phones jacks would do the trick.
I have "cobbled" together a sloppy version for use with my Bose QC-15 headset and it works quite well. The QC-15 actually comes with two connectorized cords, one with and one without the electret microphone dangling in the cord.