Part of the Cisco Small Business Pro Series, the SIP-based Cisco SPA504G 4-Line IP Phone (Figure 1) has been tested to ensure comprehensive interoperability with equipment from voice over IP (VoIP) infrastructure leaders, enabling service providers to quickly roll out competitive, feature-rich services to their customers.Supports four phone linesFull-duplex Speakerphone, headset, message waiting indicator, dynamic softkeys for phone functions4-way navigation key to easily scroll through phone features, call history directories, and on phone applicationsDedicated buttons for Mute, Headset, Speakerphone, Volume, Hold, Menu settings and Voicemail accessIntegrated Ethernet switch port to connect a computer and reduce cable costHD Voice for unsurpassed voice clarity and enhanced speaker qualitySupport for up to two Cisco SPA 500S Expansion Modules, which provide an additional 64 phone linesMonochrome backlit display for ease of use, aesthetics, and on-screen applicationsPaper label for bottom four line buttonsSupports both Session Initiation Protocol (SIP) and Smart Phone Control Protocol (SPCP)