asterisk users - Nov 2003 - prob. w/ data (modem) calls through Asterisk

I'm having major problems routing a modem (data) call through my 
Asterisk box.  I've got a single incoming POTS line through my X100P, 
and a few extensions (and modems) plugged into the ports on my TDM400P.

I've been using the system for a few weeks for voice applications and 
everything is working pretty well in that area.  But just recently I was 
trying to place a data call on one of my voice extensions (the modem is 
chained ahead of a handset on a certain extension), and the calls to an 
outside modem will not successfully complete.  When I bypass Asterisk 
completely, they complete as expected.

I figure this problem may have something to do w/ the echocancellation 
that I've read some about on the mailing list, so I tried echocancel=no 
and echocancelwhenbridged=no in addition to adding the 'd' option to the
Dial application for 'data quality'.  None of these approaches seemed to
work.  I can't even get the modems to connect, and from what I've read 
on the mailing list, most people just have problems w/ not getting top 
speeds.

Not sure where to go from here.  Anyone have ideas, hopefully based on a 
similar setup?

As always, thanks,

jl