The Cisco IP Phone 6800 Key Expansion Module (KEM) extends the capabilities of the Cisco IP Phone 6851 with additional buttons. This module adds 14 physical buttons along with access to 14 additional buttons via the page buttons, for a total of 28 buttons. The KEM supports the Programmable Line Key (PLK) function, but does not support any SIP registrations. Calls may be monitored and answered using the PLK function, but calls may not initiated from the KEM. The 6851 IP phone supports 1 KEM only