We are using Asterisk 1.2.3 with FreePBX 188.8.131.52 running in a Centos 4.7 server. All or our SIP phones are Polycom 650. We’ve been having echoing issue as far as I can remember but lately it’s getting worse. I noticed that the echo comes from calls to outside to people who use wireless headset or cordless phones. I believe it works fine for cellphones and does not have echo. We have a provider that supports our system and I’ve tried bringing up the issue to them many times but they said everything is fine. They said they have tweaked the echo cancellation and the gain to its optimun settings. I’m not sure what else to do now, can someone please help?