Types of Echo

Network Echo - the echo present when making a call using the PSTN (TDM Connections). 

How to check:  Do you hear the other person's voice echoing when you are making a call outside of your office?  You probably have Network Echo - Please read How do I eliminate echo?

Acoustic Echo - the echo you hear when your voice is reflected off of a flat surface (think Grand Canyon)

How to check:  Does your office or conference room have high ceilings and many flat surfaces?  Do you experience this echo mostly when using the speaker phone?  You probably have Acoustic Echo - Acoustic is environmental.  There is not much Fonality can do to eliminate this echo - it depends largely on the physical space you use to conduct business.

Side-tone Echo - the echo injected by a phone's speaker into the receiver as an indication that the call is 'active'. Historically this is only found on Aastra phones.

How to check:  Do you have an Aastra phone?  Do you hear your own voice in your ear?  You probably have Side-tone echo.  Please read Why do I hear myself in the receiver?

Local Area Network Echo (LAN Echo) - the echo caused by significant packet-delivery delays within the customers LAN

How to check:  Do you experience echo on inter-office calls to another extension?  Do you hear your own voice as well as the other party's voice echoing?  You probably have LAN Echo - you must consult your system administrator to check your router's Access Control Lists, Buffers, and any other security policies running on ports used by your PBXtra