A VoIP connection is different from other services. When you use your browser, for example, the only thing you need is good network speed. You will never realize if some packets have different paths or their incoming sequence is different from the source. Therefore, bandwidth is the only parameter you need to care about.
For a VoIP call, there is more to worry about.
Multi-path phenomenas or disordered packets generate echo, jitter… and so on. So the voice we hear can have a very bad quality and even come out unintelligible; leaving you and the other person you are speaking to with a less than pleasent calling experience. To test our connection quality we use TestYourVoIP and
TestYourVoIP gives you a MOS value of a simulated VoIP call (MOS scale has 1 to 5 levels. Level 5 is the best quality). You can see how these values are different for several locations and depending on what time you call. MyVoIPSpeed test shows you some connection parameters (jitter, packet loss) and the resulting overall call quality. Both of these services can be an excellent way to do pre-deployment and post-deployment VoIP connection monitoring.
If you use these tools, and you find that your problems are different from network congestion… uhm… you should probably call your VoIP service providers technical or customer care number because there might be a major problem.