Or... you can just flip your phone open, hit a fast dial number and slide the top of the phone with the speaker between your helmet and ear, and in my case it stays there, and I do the conversation and then put the phone back in my shirt pocket. I keep it on Vibe when I'm on a trip so I can feel a call.
Most that I've talked to would not believe I'm on a bike trip somewhere at highway speeds. Works for me.
You mileage might vary if you have a full face. I have a Nolan N102 on the Wing and wear a Mx style helmet on the KLR. The Noland I have to flip up, but on the Mx helmet I go from underneath.