If it is acoustic, sometimes lowering the volume of the earpiece helps. Most cordless phones are much more sensitive (better microphone, better circuitry) than the cheap or older corded phones. Many also have the abililty to boost earpiece volume by a large factor. Think of what happens when a person using a public address system gets their microphone too close to the speakers or has the volume up too high. The squeal is made because of the time it takes for the sound from the speaker to reach the microphone and be sent back to the speaker. With a VOIP system you have a much greater delay than just the few milliseconds in a PA system. That is why you hear the echo instead of a screach. By turning down the earpiece volume or buying a newer DECT 6 hi-quality phone you can usually get rid of echo caused by acoustic coupling. I have a newer Uniden 1580-5 that has 5 handsets and was on sale for $80. It works great and even has a good quality speakerphone and allows several handsets on the same call.
If the echo is coming from the VOIP source itself, then there is nothing that you as a user can do - except make it easy for ooma to put the fix into motion. Capture all of the offending calls in a log - time, date, number called, incoming or outgoing, severity of echo, etc. Then when you have 10 or so of the calls logged, call ooma. Ask to have a ticked created for a higher level technician and be ready to supply the log to that more senior tech. They can check their logs against your log and determine routing, etc. In my case, they did some work with their "partners" in my area to change routing, add echo cancellation, and other stuff that I really don't understand. The bottom line is that my service is now stellar and has been for about 8 months.
It is worth the effort to gather the information or make the equipment changes - I used to pay the big bucks for a long distance package and a second line. Now all I do is sit back and smile I make free calls with ooma!
