app for Drs. on call

[merryman]

Hi- I am a veterinarian, and am often on call for several consecutive days. Towards the end of it, I am very sleep deprived but I can't turn my phone off in case there is an emergency. However, I would prefer to not hear the phone ring when anyone else calls. Is there an app that would allow for all calls to go directly to voice mail, save a few important callers?