I have found that the mic on my headset (Denon AH-600) which has worked for me on all other android smartphone I have tried, including the SGS4, does not work on this phone. The only headset I have been able to get working properly on this Relay is a pair of Samsung earbuds w/mic that came with that SGS4.
Is this a known issue on the Galaxy Relay? Is there a fix for this? Thanks!