Generally, poor call quality is a result of an issue with the internet connection.  There are multiple tests you can conduct to test your internet connection.

 VOIPo provides a utility for testing that can be downloaded here.  If you are having call quality issues, please run this utility, select option 2 for a detailed test, and email the created text file with the results to support@voipo.com.

 There are also third party speed tests that you can run.  While VOIPo does not endorse or have any affiliation with these tests, the following are popular:

www.speedtest.net

myspeed.visualware.com

 If your internet connection appears to be functioning normally and you continue to have call quality issues, please contact support by emailing support@voipo.com or visiting support.voipo.com and submitting a ticket.