I had to give my mobile number to my patron. He doesn't do voicemail and I can't just turn my phone off. I'm expected to be available 24/7, and if I can't answer the phone send a message immediately explaining why. He goes livid when he thinks I ignore his calls. Oh, and I'm on android.

Is there an app that I can set up to run from a certain hour to a certain hour which will refuse calls and send a prewritten message (ex. Sir, I can't pick up the phone because...) ? I don't think he'd be tech savvy enough to see through that. He's ancient.