Businesses dealing in telephone apparatus supply equipment used to make and manage voice calls over landline, mobile or internet-based networks. Products may include corded and cordless telephones, desk phones, conference phones, headsets, answering machines and accessories such as cables, chargers and compatible power supplies. Some suppliers also provide business telephone systems, including private branch exchange (PBX) equipment, extensions, call-handling consoles and hardware for voice over internet protocol (VoIP). Services can include advice on choosing equipment, installation, configuration, repairs and maintenance. For business systems, this may involve setting up handsets and extensions, connecting equipment to existing networks, and arranging features such as voicemail, call transfer or conferencing. The range varies: some businesses focus on retailing individual phones and accessories, while others supply and support larger office systems.