I had a referral from an associate to a doctor who needed a "phone tree". He needed to have a caller make a selection to reach different people in his offices. The phone tree he described started with the basics:

Routing for IT support calls can be hard to manage. Internal phone systems can direct calls to an extension when someone makes a selection. And it may be able to ring several phones at once so all of the support staff can take turns with calls. But after hours are a different issue. Routing calls to a single phone after hours may not be a good option. Rotating calls to the support staff cell phones is the solution.