Only the advertisements will be unmutable.
We are planning on having a sound clip which asks the player to type a special command in the console. It will play randomly every hour or two while you are in game, and there will be some sort of penalty for those who miss too many of them. That way we do not have to mess with client volume, and people can not get around the new system by unplugging their speakers.
It would have some leeway, maybe 2 or 3 free misses a week? Numbers are forthcoming.
Also, we would of course flag your character as exempt if you provide us with a copy of your disability card, or a note from a doctor stating you are legally deaf - with the doctor's office phone number of course.