I am asked from time to time why I don't carry a cell-phone.
The answer is simple: My clients don't have emergencies.
I don't plan for them to have emergencies; I plan for them NOT to have emergencies.
I plan for them to be confident in coping with minor hiccups, and I respond to phone calls and emails as soon as I return to my office.
Of course, not having call-display helps; when the phone rings, I pick up the phone, so most would-be-emergencies are nipped in the bud.
Take a good look at your clients.
Have you made them strong and self-sufficient, or are you one of those parents who is reluctant to let "Little Johnny" leave home until he is over 40 years old?
Good parentage builds children who are economically viable by age 20.
Good service providers build clients who are self-supporting in all manner of day-to-day events.