This is a new non-OEM replacement handset designed for and compatible with the Cisco 7800 and 8800 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:

7811

7821

7841

7861

8811
8841
8845
8851
8861
8865