Skype for Business Standard vs. Enterprise feature matrix https://kb.smarshmail.com/Article/2245

Intermedia architected their cloud specifically for reliability, performance, and data protection.

A 99.999% uptime SLA means that you should expect less than six minutes of downtime over the course of a year—and, if this should fail to be delivered, you'll be compensated for it.

Our competitors only offer a 99.9% uptime guarantee. That's just three nines. And while that difference may not seem significant, the difference actually amounts to downtime of over 8 hours.