Developer on Call
Kayak.com co-founder Paul English on this topic (2010):"The engineers and I handle customer support. When I tell people that, they look at me like I'm smoking crack. They say, "Why would you pay an engineer $150,000 to answer phones when you could pay someone in Arizona $8 an hour?" If you make the engineers answer e-mails and phone calls from the customers, the second or third time they get the same question, they'll actually stop what they're doing and fix the code. Then we don't have those questions anymore." 
https://www.inc.com/magazine/20100201/the-way-i-work-paul-en...(This is of course a bit different thing, probably he's not suggesting to having those engineers take the calls middle of the night).