Using the USB host adapter you should be able to plug in a bluetooth headset or microphone. Will it work? I couldn't tell you as I haven't tried it myself. I do know that keyboards, mice, and USB storage of up to 16GB are apparently supported.
The 7042 has a built-in microphone, a pretty good one too. If you look at the side with the connectors on it, there is a hole between the headphone jack and the hdmi connector. That some say is the microphone.
I tried talking tom and it works fine on my 7042. Try another app that uses the mike.