I've seen a few posts here regarding latency and wanted to post some of my learnings in hope that they may help others. I don't make any claim that I'm an expert. As a matter of fact, some of my learning may be flawed. So, I'll just say that I'm some guy who's stumbled through this and learned a few things that he finds interesting along the way.
Latency can be frustrating and somewhat systemic in VOIP services. I was experiencing problems talking over people with Ooma so I switched to an OBI Device where I started comparing providers. I've spent alot of time measuring latency between providers and there isn't a silver bullet, however I thought I'd offer a few things that might help others in trying to troubleshoot this in their own.
1) First, since a lot of people use Google Voice I thought I should point out that Google Voice isn't necessarily a world class VOIP provider and may have more variance in service quality from time to time versus a provider who only does VOIP such as Anveo, Voip.ms, etc. I've seen more fluctuation in my Google Voice service than any other provider, however that being said it tends to have great overall latency.
2) A lot of people call echo test lines to measure latency. If you're calling any service not hosted by your provider, you need to remember that your subject to additional network components that are really outside of your (or your providers) control. Case in point, I get drastically different results using the echo test number 206-456-0649 vs 909-390-0003. These are services running on different networks and since they are sending audio back, you need to remember that you're also subject to return latency.
So, if you are experiencing latency calling a specific echo test number it may not actually be a sign of a wider problem. If you think you have a latency problem then I'd recommend measuring a few different ways to really get an accurate picture of whats going on.
I've done a number (ok, hundreds) of echo tests comparing a number of providers and thought it would be useful to share my results.
Methodology: I called 3 different #'s and did a "pen tap test" to measure latency. This approach is detailed (along with a video) at this link: http://goo.gl/jGtX0V (http://goo.gl/jGtX0V) -- but basically you call an echo test service, put your phone on speaker, tap a pen against the phone all while recording the sound on your computer. You then time the gap between your tap and the return tap to measure latency.
I've compared the following services three different ways. First, I timed latency using the 909-390-0003 echo test line, then I used the 206-456-0649 (option 3) echo test line and finally I just called my cell phone and instead of measuring the echo I simple measured the time it takes for sound coming through my phone to play through whatever OBI Connected service I dialed.
Here are the results I gathered by averaging three separate phone calls to three separate services using 6 different providers (your results may vary depending on a multitude of factors)
Google Voice:
Average latency calling the 909-390-0003 Echo Test Line: 616ms
Average latency calling the 206-456-0649 Echo Test Line: 1169ms
Average latency calling my Cell Phone (TMobile): 370ms
Circlenet:
Average latency calling the 909-390-0003 Echo Test Line: 885ms
Average latency calling the 206-456-0649 Echo Test Line: 923ms
Average latency calling my Cell Phone (TMobile): 396ms
Anveo:
Average latency calling the 909-390-0003 Echo Test Line: 817ms
Average latency calling the 206-456-0649 Echo Test Line: 888ms
Average latency calling my Cell Phone (TMobile): 432ms
Voip.ms:
Average latency calling the 909-390-0003 Echo Test Line: 753ms
Average latency calling the 206-456-0649 Echo Test Line: 884ms
Average latency calling my Cell Phone (TMobile): 489ms
Ooma
Average latency calling the 909-390-0003 Echo Test Line: 1326ms
Average latency calling the 206-456-0649 Echo Test Line: 992ms
Average latency calling my Cell Phone (TMobile): 613ms
Bonus: VOIP at my office. I don't know what provider we use, but I work for a large (publicly traded) company with a sizable IT organization and I'll assume we are finally tuned. These tests were performed using Cisco Office phones and not an OBI.
Average latency calling the 909-390-0003 Echo Test Line: 546ms
Average latency calling the 206-456-0649 Echo Test Line: 662ms
**Average latency calling my Cell Phone (TMobile): 502ms
** Its worth noting that since this test was performed in the office my phone was in a different area (different towers) than the tests above.
TL:DR; Results vary between provides and the numbers you call. You'll need to consider several factors when trying to understand if you have a latency problem. The best test of all is experience - If you aren't talking over people and having a hard time holding a conversation then you probably don't have an issue.
Sorry for the long post, but hopefully it helps someone!