The 20S is very good about not picking up background noise, but it isn't perfect. A large part of why I bought the unit is to attend conference calls during my long commutes into some of our locations. It never occurred to me to check for a mute option since every Bluetooth adapter I've ever owned (granted, this is the first motorcycle unit) has had the feature. At this point I need to consider buying a handle bar mount for the bike (not a thrilling option since I don't trust the phone will stay in it and worry about water) and riding without gloves so I can swipe my screen. A mute feature would be an ideal addition.
Feature request: Mute