A good way to start a virtual office is to use Google Calendar. Google Calendar is a piece of free professional software that allows you to set up calendars and schedules easily for all employees and track them all at the same time. It can even be used offline.
Another piece of software that can help is WebEx. WebEx allows free users to have virtual meetings online with up to three people. FreeConference is good alternative to WebEx that allows up to 150 people to make four hour calls. To help with building a virtual office you'll also want to hire a virtual assistant or receptionist.