BlueAnt Interphone all the way. Works with my mp3 player, works with my phone, and it works for intercom between me and a riding buddy. Love it, perfectly loud, perfectly comfortable, perfectly easy to install.
I mostly just use it for the phone. I try not to talk on the phone while i'm riding but it's a whole lot faster to answer the phone and tell them you are busy then it is to pull over to the side of the road every five minutes and take off your gloves stand up reach in your pocket fish out your phone dial a number.. take off your helmet or scream through your visor.. weak...
Interphone is the way to go for sure.