The Aastra 51i (6751i) offers features and flexibility in an open-standards based, carrier grade basic level SIP phone. With a sleek and elegant design and LCD display the 51i terminal is fully interoperable with leading VoIP Telephony platforms, offering advanced XML capability to access custom applications and support for high-quality SIP communications. Part of the 5i Series of IP phones, the 51i is ideally suited for light use small and medium business applications such as lobbies or common areas , where single line high-quality SIP communication is required. Sold without power supply (Aastra AC Adpt. 31i - 5xi - 6739i). It is used to provide power when in-line power over Ethernet is not available.