The Cisco CP-6851-3PW-NA-K9= 6851 IP Phone with MPP Firmware has 4 SIP registrations and support for 1 Key Expansion Module. The Cisco 6800 Series with Multiplatform Phone (MPP) is a cost-effective portfolio to improve communications and reduce operation costs on Cisco Webex Calling, Webex Calling Carrier, Cisco Broadworks, and approved Unified-Communications-as-a-Service (UCaas) platforms. 

• The 6841 and 6851 have a white backlit, grayscale, 3.5-in. (9-cm) 396 x 162-pixel display.
• The 6841 and 6851 supports either a narrowband or a wideband audio handset connected
  through an RJ-9 port.
• Backlit indicators on the audio path keys (handset, headset, and speakerphone), mute key, select key, line keys, and message waiting.
• Can be wall-mounted using the optional 6800 Series wall mount kit (sold separately).
• The 6821 and 6851 support IEEE 802.3af PoE (Class 2); power consumption does not
  exceed 6.49W.
• The 6851 and 6871 are compatible with the Cisco Unified IP Phone Power Injector (CPPWR-INJ), and with the Cisco Aironet® Power Injector (AIR-PWRINJ5=).
• and more!