The Sennheiser Electronic Hookswitch for Cisco 8900 & 9900 Series Phones connects any Sennheiser wireless office headset to 8900 and 9900 series Cisco phones, allowing for remote answering and ending of calls without the use of a handset lifter. Call us at 1-800-HEADSETS (1-800-432-3738) to check for compatibility with your phone.