HTC 8125 / 8100 / MDA (USA) / K-JAM / P4300 (Wizard)

Spec says it supports stereo. I assume the same jack can be used with a wired hands-free headset. Anyone know how this works? Are there four nodes on the 2.5mm plug to accomodate a stereo hands-free headset(eg. Shure i3C) Or, perhaps does is allow "either" a mono hands-free headset OR stereo headphones(without mic)? Any ideas?
Thanks in advance!