Actually Steve, I have come to the conclusion that allowing my patients to use outside messaging during work is better than back in the day when a staff member had to get another staffer out of a room to tell them that a spouse was on the phone wanting them to pick up milk on the way home. As much as I may have tried to limit personal phone use it got to be comical when, after hearing her say things like "I already told you you are not going out with him so forget it", I would step out of a room and the receptionist (who is no longer in my employ)was actually on the phone with her daughter and would quickly say something like "Ok, then, I have you down for your appointment next week".
Now, I may walk out of a room and note an employee chatting with someone on Yahoo but they know their chat history will be monitored. I have been known to walk up behind them and read the chat box over their shoulder or, if they have minimized it, maximize it and read everything there. I figure, "My machine, my office, my right to read anything". So, for the most part, they know not to abuse it or take advantage of me. Of course my current employees have been around with me for a long time so we basically know most everything about each other anyway.