Echo issue on analog PBX

I am experiancing an echo issue on my Asterisk system, and I have searched the forum several times and haven’t found a definitive answer to my problem.
The problem is that I am receiving an echo on all of my handsets/extensions. The echo is by far more pronounced on my GE DECT analog handset than others (even attached to the same FXS). No problem, just turn on the echo canceller, right? Not quite.

Here are my system stats:

System make/model: IBM Netfinity 6000R
CPUs: 4-way Pentium III Xeon, 700 MHz per CPU
Hard Disk: 18 GB Raid-5 array (IBM ServeRAID hardware RAID contorller)
Memory: 1.5 GB PC100 ECC Registered SDRAM
Telephony interfaces: Digium TDM410P, Openvox A400P; total 1 FXO, 5 FXS (the FXO is on the Digium card)
Network: IBM 10/100 on-board Ethernet
Asterisk version: 1.4.x
Linux distro: AsteriskNOW 1.0.x (slightly modified)

Before I go any further I want to state that yes, I am using AsteriskNOW, however I’m posting here because I use it as full-on Asterisk, and only chose the AsteriskNOW distro to speed up the install (my preferred distro is a very old version of Mandrake… It isn’t worth the effort of upgrading a kernel 2.2 OS to the level of being able to build Asterisk and Zaptel)

Now back to the issue…

The problem is my DECT handset appears to be incompatible with the echo canceller (the channel rapidly becomes “choppy” and eventually fades to silence). Adding the following code to zapata.conf removes the echo, but causes the above problem

echocancel=512 echotraining=yes

I have tried adding this code to the trunk in users.conf, while defining no echo cancellation on the extensions, but it does nothing to remove the echo (though it prevents the DECT sets from “dying”).

I haven’t ruled out a problem with my wiring or simply that I have crappy handsets (I also have an Aastra analog set on the same extension, and though I can tell that the echo is there it’s barely noticable).

Am I doing something wrong here? Thanks.