[Asterisk-Users] Polycom 501 horrible echo

[Jeff Herring]

I have the following situation:

Asterisk 1.2.1
25+ Polycom 501 telephones. Bootrom 2.6.2.0032 Application 1.6.2.0041
Some 501's local to my network, some across the great INTERNET divide.
PRI connected to Sangoma card.

Issue: horrible echo (and squeals, and "underwater-like" sound) on speaker
phone when calling from extension to extension.

echo not present when calling outbound using PRI or when receiving calls 
from PRI.
echo not present when using handset or headset in any case.

All gains, etc. are as listed in the Polycom Admin Guide.

Not specific to any phone, or its location on our network.

I suspect the issue is related to the echo cancelation HW in the speaker 
phone, but
I'm not sure...The unfortunate thing is these phones were purchased because 
of their
excellent speaker phones which now appear to be worse than the Grandstreams!

Anyone with thoughts of where to start?

TIA - Jeff H.