Denti, yes I have recently started using a smart watch. I have it connected to my own personal phone rather than the company one and is brilliant.
As you say, I can have the phone muted and not miss calls/messages.
I have finally gone for the "gunge up the switch" option on the callout phone rather than using a case. I'm sure I can pick out the silicone sealant if necessary, and I'm pretty sure my company would rather me not miss calls.