Latency

You can test the latency of your internet connection with ping or traceroute. For example:

$ ping -c 1000 -i .2 sip.ca1.link2voip.com

When the test is done, you will see something like:

--- sip.ca1.link2voip.com ping statistics --- 1000 packets transmitted, 1000 received, 0% packet loss, time 204829ms rtt min/avg/max/mdev = 26.071/37.636/458.223/28.421 ms, pipe 3

If you do this a few times a day, over several days, and your avg is under 130ms and you have 0% packet loss, you're ready for VoIP. If not, call your internet service provider (ISP) and ask them to resolve the issue.