A PBX system is a private telephone network that connects multiple extensions within an office and to a small number of outside lines. It can deliver business telephony features such as call forwarding, transfer, queue, auto-attendant, and voicemail . A PBX system can be made up of hardware and software that work with communication devices such as telephone adapters, hubs, switches, routers, and telephone sets. The size, complexity, and cost of a PBX system can vary depending on the needs and preferences of the organization.