I have always given out my cell phone number to clients. In almost seven years of practice, I have never once regretted doing this. I even did this as a public defender when I had far more clients than I do today.
As a public defender, I looked at it this way: Despite multiple prompts, most of the people I would represent on a given day would not have come into the office for an interview. Why wouldn’t I make it easier for one of those people to contact me?
You can always turn the phone off. You can also tell people when they have reached you at an inconvenient time.