Hey angry gerbil seems like you have the most insight to this job. I've got a question as far as ambient noises, how much do you have going on in background? And outside of your room that the phone can or can't pick up? Hope that makes sense.
The headset mic seems to be pretty good at screening out ambient noise as long as you're not blasting dubstep at 100+ decibels. I have NPR playing at a low level in my office during work and it's fine. I'm out in the country so there is very little noise outside my office beyond birds and my dog that is barking at said birds.
I'm really not sure how much noise you're talking about. If you're in the city and have a construction crew running a jackhammer outside your building... that may not work out so well.