Strong echo OpenVox G400P, Elastix 2.3. How to win?

Question

Asterisk

Good afternoon.
Need help with Asterisk (Elastix).
The situation is this: we have an OpenVox G400P GSM gateway (PCI-E card with an MTS sim card), Elastix 2.3 and phones (all Yealink companies)
when making calls within the network (between our phones) - the sound is excellent.
when calling to cellular / landline - a crazy echo, which can not be defeated in any way. and the echo is only on our side. the client on the other side of the line has excellent sound.
the most interesting thing is that the echo sounds throughout the conversation and insanely interferes with communication. BUT! the recorded call does not contain an echo (for some reason). that is, if we reproduce the recording of the conversation - there is no echo. but during the conversation there is! and only for calls (incoming\outgoing) voip <-> urban\cellular.
In the settings of the gateway itself (Hardware Detector -> Configuration Of Span), various echo suppressors were set - OSLEC, MG2, etc. Nothing helps. In the chan_extra.conf settings, we played with the echocancelation parameter. In the settings of the handsets themselves, echo suppressors were turned on. Even PBXMate Addon was installed and an echo-canceler was included in it. The most funny thing is that nothing has changed (nothing at all - no more, no less, as if nothing was included). Wherever that is not included. Apparently we're doing something wrong? Maybe it makes sense to buy another gateway (with hardware G168 echo cancellation)?
In short, we need advice from much more experienced users.

Answer 1

Read more about echo. Learn that the echo is the problem of the one who hears it.
Those. it occurs in your devices. Or in the transition SIP analog.
But I would dismiss the second option - then there would be an echo in the recording :)
The gateway has nothing to do with it, just like the far side.
Check the phone settings, try to put the softphone to check, Another device, such as fanvill or grandstream.

Answer 2

The question is - have you tried to look for an answer to the question on the OpenVox forums and follow the recommendations for eliminating the echo? It is possible that echodaw works for you at the same time in both Asterisk and Openvox