Uptime

Uptime (or availability) measures the share of time a service runs normally, excluding outages. It's expressed in "nines": 99% availability is about 3 days 15 hours of downtime a year; 99.9% ("three nines"), about 8 hours 46 minutes; 99.99%, barely 52 minutes. The climb is steep: each added nine divides the acceptable downtime by ten. The caveat that goes with it: a global figure says nothing about when the outage hits — 8h46 of downtime at 3 AM and 8h46 on a Monday morning don't cost a business the same.

For a phone service, the useful question isn't "what's your uptime?" but "what exactly does it cover?" The web platform can be green while call routing fails; messaging can work while the auto-answer is down; are planned maintenance windows counted or excluded? A serious provider publishes a status page readable in real time, separates what's covered from what isn't, and warns before a maintenance — not after. What isn't measured doesn't improve; what's measured badly sells well.