asterisk users - Sep 2004 - No Echo Cancellation with echocancel=yes

hi, 

i've got big problems with the Echo Cancellation of Asterisk. Entering
"zap show channel 1" (while telephoning / making a call) gets me this
line:
"Echo Cancellation: 128 taps, currently OFF" 
And there's a heavy echo noticeable. 
When I'am called, Echo Cancellation is enabled, and there's no echo
noticeable!

This is my setup:
ISDN(DECT)-Telephone <--> Asterisk <--> SIP2PSTN-Gateway

I'm using the most recent bristuff-version (1.0rc04a); this is my
zapata.conf:

[channels] 
switchtype=euroisdn 
signalling=bri_net_ptmp 
pridialplan=local 
echocancel=yes 
echocancelwhenbridged=yes 
immediate=no 
overlapdial=yes 
group=1 
context=default 
channel=>1-2 
	

Would be very nice if someone is able to show me how to enable Echo Cancellation
(when making calls)!

Thanks in advance, 
Sion