While in the waiting room at the dentist's office, I noticed a sign at the doorway that leads into the patient rooms, saying "No cell phones beyond this point".  

I asked the receptionist if I needed to leave my phone with her during the appointment.  She said "No, just don't let it ring while the Doctor is working on your teeth, or he'll stop, and ask you to leave."   I said "Really?"   She said the dentist was tired of people reaching for their phones while he was working on them.   I thought - I finally have an out!

But then asked, "If he drilled my tooth, and hadn't done the filling, would he still stop working on it?"   She told me that I probably wouldn't want to find out.   So I sat in the chair with my phone on airplane mode, and there was no incident, just pain.