It is important that you are able to have good call quality. Is this only happening on the network Extender when you have multiple calls? Is your network extender connected to a landline internet connection that is getting at least 10mbps download, and 5mbps upload speeds? How long after you terminate the second call does the voice continue to be distorted? is it for the entirety of the first call, after the second call is terminated, or does it eventually return to normal?