The document discusses CenturyLink's Hosted VoIP service. It begins by explaining what VoIP is and how it works. It then defines a PBX and explains that CenturyLink Hosted VoIP replaces the need for an on-site PBX by providing those features through their network-based platform. The document goes on to describe how users connect to the CenturyLink network to use HostedVoIP, what equipment is needed like IP phones, how administrators and users manage features and settings, and provides additional details on pricing and features.