Also, CUCM does not participate in the audio path and therefore cannot impact echo. There are no settings to control this on an IP Phone although you should verify the problem exists without a headset connected (incorrectly set analog voltage/ohm settings headsets offer to support multiple PBX systems frequently cause this).
All echo cancellation and controls are done on the analog/TDM gateway. Start with this doc:
http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080149a1f.shtml
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