This is a new non-OEM replacement handset designed for and compatible with the Cisco 6900, 8900, and 9900 series of IP phones.  If your calls have poor sound or people are saying they can't hear you the problem may be your handset, this will replace it.

These models of Cisco phones are compatible with this handset:

6901

6911

6921

6941

6945

6961

8941

8945

8961

9951

9971