My speedtest results with the system fully loaded
I'm guessing that the 300ms ping could be a problem with VOIP. But that was fully loaded, so it might be fine under light loading.
The 'jitter' problem I referred to - in a VOIP (or cell phone), they take a snippet of sound, digitize/compress it into a 'packet' and then transmit that packet to the receiving end. Over the internet, each packet takes whatever path is available, it's all very dynamic routing. So a packet sent at one point will sometimes arrive later than one sent earlier. This isn't a noticeable problem on a web page. The page loads in a second or two, and you really don't care much what loaded first.
But with voice, if sequential packets of sound don't arrive in some reasonable time, they have to just drop that snippet. You can't wait a second for it to show up. This is one reason why there is a noticeable delay in VOIP (and cell phone if you listen for it). The delay is required for the time it takes to sample enough sound to compress, then transmit it and allow for some 'jitter' in arrival times of the packets, and then re-construct it all at the receiver.
It's a miracle this works at all!
Anyhow, I suspect that jitter is generally pretty closely related to long ping times. Or at least some X amount of jitter is going to be more of a problem if the ping time average is already high - the system can only wait so long.
I've got rather marginally 'high-speed' internet. At best I get 3Mbps down and 1Mbps up, and 20-30 mSec ping times, but it varies all over. My VOIP is fine 85% of the time, and the other 15% is up for grabs, from mild chopping to unusable and dropped calls. I use a local point-to-point wireless provider, which means I don't need to deal with a monopoly, which does more to keep my blood pressure in line than the meds I take.
-ERD50