We don't have an office, everyone works from home all the time unless we decide to all work from someone's home for a few days. If we do need an office for a day or two, we rent an office for a few days, but we've only done that for 3 days in 2017.
All company telephone numbers are routed to private cellphones, most calls are done via Skype and all internal communication via Slack.
Our "office" is completely virtual.