The company I work for makes and supports bespoke software for a wide range of clients, employing roughly 30 people. We are open from 9-5 and by default provide

The company I work for makes and supports bespoke software for a wide range of clients, employing roughly 30 people. We are open from 9-5 and by default provide no support outside those hours. The only exceptions are incidental, well communicated and seen as a logical part of our jobs (for example, a big coordinated release of a new application in the weekend outside business hours). We host 95% of the applications that we create at our sister company which exclusively does hosting where there is an on-call system, but it is only available to their largest customers and only by request. Of course company-wide alerts (an entire router that goes down, degraded storage, etc.) do garner an on-call response.