Well, I'm far from what anyone would consider knowledgable...

We use GBH phones and accessories. One thing I DO know is that their speakerphones are good enough to pick up my muttered comments during teleconferences. Embarassing on more than one occasion.

You might be able to rig a headset up using a voice tube, what are you trying to amplify by using a microphone? Voice or instrument? A tube could be bent fairly closely to whatever instrument you were using.

Check out their accessory link, they have the voice tubes, as well as cables to connect and record phone conversations, microphones, etc.

Best of luck,
~Jen