Once you have run the test you should see your Download and Upload speed results. The lowest speed will be the limiting factor in your call quality. Here is what you could expect if either of your speeds are too low:

Upload speed too low -> Your voice will not be clear to people you call.
Download speed too low -> Your callers voice will not be clear to you.
Latency -> The time delay between when audio is sent and received.

We recommend a minimum of 128Kb/s for both upload and download speed for voice lines, and a minimum of 400KB/s if you have enabled the fax option. The more speed the better especially when you have addition things using your Internet connection like PCs, notebooks, game systems, etc. Using these things in conjunction with your digital phone service can affect call quality so we recommend you upograde to a more generous bandwidth plan from your ISP.