A Private Branch Exchange (PBX) or a Private Automatic Branch Exchange (PABX – which is out of fashion since all modern day PBXs are automatic), is a phone switch serving a business or organization and is usually located on the organization’s premises. The PBX provides phone services including internal calling, and access to the public switched telephone network. It allows a small number of outside lines to be shared among all of the people of the organization. Advanced PBX phone switches sometimes provide auto-attendant, voice-mail, and ACD (automatic call distribution) services for the organization.