asterisk users - Jan 2005 - Echo problem - (sorry if this is an nmf question)

I recently installed * on my firewall and that of a relative some miles 
away.  I route sipphone
(kphone and x-lite) calls from deep within the backbone (two layers of 
firewall) on each end to the other.  Works fine between @200Mhz pentium 
doorstop linux boxes (even w/2.4 kernel).The problem of course is the 
output of the speaker at the other end is picked up by the microphone 
(confirmed by switching to headset eliminating echo on opposite end).
Before I dig into doc of x-lite/kphone I thought I would try asking here 
for a solution other
than simple using headset at each end.  (would like to have the speakers 
"ring" to let
folk know there is inbound calls so they can hear when they are not at 
the computer)

(and yes, the next step is of course to actually buy some hardware so 
that all the house
phones can make voip calls in addition to pots which eliminates this 
problem, but that
is probably not in this quarter's budget.)