A business phone system is expected to provide standard features like conferencing, voice mail and an automatic attendant, as well as additional ones like directory services, integrated messaging and unified communications. They come in four distinct versions: non-key system telephony, key systems, private branch exchange (PBX) and the much-touted voice-over-IP (VoIP) systems.
Non-key systems, similar to residential phones, have the advantage of being inexpensive and stand-alone, so they can easily be moved around. They have a central key system unit (KSU), which provides functionality unavailable on residential phones.
Most commonly used are PBX systems or PBX-key system hybrids. PBX systems can be expanded by increasing the number of ports, or connections that can be made at one time to the central system. Many large organisations continue to use these legacy systems, though the move towards converged telephony and unified communications is beginning in this segment. Legacy systems are designed to be highly reliable but are not necessarily equipped to handle the advent of new technology such as e-mail. Unified communications means that multiple applications are supported by a single platform, specifically the Internet or over a company-wide network.
A VoIP telephony system makes the best use of bandwidth to provide cost savings, greater productivity and advanced features. As an example, personal numbering that can provide mobility to employees. Every user is assigned a unique personal number that a caller will dial. The software will route the call to the actual phone that the user is currently connected to, regardless of location. So the user may receive the call on a mobile phone, a PBX extension or on a home phone, anywhere in the world.
Converged systems that rely on a company-wide network, or IP-PBXs, are seeing greater usage. But the more important shift seen in this area is freedom from any hardware or software lock-in from vendors, giving autonomy and flexibility to IT managers.