asterisk users - Jun 2007 - DTMF Problem with one sip trunk and two carriers

Hello,

I got a little problem here. My Setup is like this,

Service provider  ->  ser ->  asterisk -> termination provider.

I have a sip trunk on asterisk pointing to ser,

allow=ulaw&alaw
context=from-trunk
disallow=all
dtmfmode=inband
host=ser ip address
insecure=very
type=peer

This works with One service provider. Now we are setting up a contract 
with another service provider, inband dtmf does not work. If I change 
the dtmf to rfc2833, it works with second SP but does not work with 1st 
one.

What can be work around for this.
how can I setup two trunks with different dtmf and same ips.
Is it possible to run single instance of asterisk on two different ports 
and then I create two trunks, on listen on port 5060 and another trunk 
listen on port 5061. That was I can send call from ser on two different 
ports.

These are just few thoughts, I am open to suggestions.

Thank you,

-JK