Ok, some little news. Today I tried a N95 headset with my N900 and vice-versa. Both headset were working flawlessly with the "non-respective" device (except for the "headset" icon on N900 -- to get i have to plug in the headset and then turn on the device; a further unplug & replug doesn't make the icon come back), with working headphones AND microphone. Could it be a software issue, at this point?