IP PBX is designed to provide similar functionality to that of traditional PSTN-based PBX systems. IP PBX can be built or provided by a telecom operator, a third-party Internet service provider or it can be hosted in-house. Unlike PSTN PBX, IP PBX has the ability to switch, forward and route the calls between VoIP networks to PSTN and PSTN to VoIP. IP PBX services are largely delivered and managed through purpose-built software with supporting switches and network devices. Hosted PBX and virtual PBX are among the delivery modes of IP PBX system.