Some time ago, I noted that there was a walkthrough of the original Microsoft Building 3. If you go behind the receptionist desk, you’ll see a telephone at the receptionist’s station, but off to side, there was also a red telephone resting between a tape dispenser and a small pamphlet labelled “Quick Reference Guide”.

What was this red telephone for? Was it a direct line to Bill Gates’s office? Or maybe it was a direct line to Security?

Nope.

It was just a plain telephone.

And that’s what made it special.

As is customary at large companies, the telephones on the Microsoft campus were part of a corporate PBX (private branch exchange). A PBX is a private telephone system within a company, and companies use them to save on telephone costs, as well as to provide auxiliary telephone services. For example, you could call another office by dialing just the extension, and the call would be routed entirely within the PBX without having to interact with the public telephone systems. Generally, most calls are typically from one office to another, so a PBX saves considerable money by reducing demand for outside communications services. Also, a PBX allows integration with other systems. For example, if somebody leaves you a voicemail, the system can email you a message.

But what if the PBX is down, and there is an emergency?

The red telephones are plain telephones with standard telephone service. They are not part of the PBX and therefore operate normally even if there is a PBX outage. If there is an emergency, the receptionist can use the red telephone to call emergency services. Presumably, each red telephone was registered in the telephone system with the address of its building, allowing emergency services to dispatch assistance quickly.

Bonus chatter: What was the “Quick Reference Guide”? It was a guide to emergency procedures. It makes sense that it was kept next to the emergency telephone.

Bonus bonus chatter: Bill Gates kept a red telephone in his own office as well. If the PBX went down, I guess it was technically true that the red telephones could be used to call Bill Gates’s office.