My Boss's Free Haircut - S4-E20
Corrected entry: Cellular phones are not allowed at hospitals because they can disturb sensitive equipment. While Kelso might not recognise his patient's "toy" as a cell phone, Laverne obviously does, and she doesn't react on it being forbidden.
Correction: Many people use mobile 'cell' phones in hospitals, even the staff, and so a lot of them don't react, besides the fact that this is a character's choice.