Wikipedia
VirtualPBX is a privately held communications service provider that pioneered the type of private branch exchange (PBX) technology called a virtual or hosted PBX.
A business uses PBX technology to manage phone tasks such as call routing, allowing more than one person to be reached from a single number, voicemail, faxing, automated greetings, conference calling, and sending phone calls to the first available person in a department.
A hosted PBX offers remote office users, small businesses, and home-based businesses an alternative to purchasing, installing and maintaining their own PBX hardware on site. This approach allows these companies to have access to similar features that a larger company would without the high costs associated with the purchase of on-premises PBX equipment.
Recognized as one of the leaders in its market, Virtual PBX’s services make use of traditional public switched telephone network technology as well as VoIP technology. Virtual PBX also provides a service called PBX Parachute, which gives companies that own an on-site PBX a disaster recovery backup capability to keep their phone service running in case a power failure disrupts local service.