Bear in mind that the value is in being highly responsive, not instantly reachable. You’ll screw up your life if your cell phone number is in thousands of hands and those people feel they have the right to call at any time, and you enable them by taking the call.
I walked away from a guy who took a call while we were talking at a convention. The person in front of you is the important one. Brain surgery, perhaps, can’t wait for a few hours. Nearly everything else can.