asterisk users - Jul 2005 - Can Asterisk pass through SIP status codes transparently?

Hi,

I'm reasonably new to Asterisk and have a question which I hoping somebody
can help me with. I've looked through the archives and config guides, etc
but unfortunately I can find no mention of the information that I'm looking
for.

I have an Asterisk server running version 1.07. On the user side there are
several Grandstream phones and two 24 port fxs gateways. Asterisk is configured
to send outgoing PSTN traffic to a SIP to ISDN PRI gateway.

When an outgoing call is unsuccessful for any reason (busy, congestion, wrong
number, etc) the SIP/ISDN gateway sends back a SIP status code to Asterisk.
Asterisk then sends a status code of 486 (busy here) to the user devices
irregardless of the SIP status code that it received from the SIP/ISDN gateway.
I can chnage the code that Asterisk sends to 503 by modifying the macro
outisbusy and setting outisbusy to send a congestion status code instead of a
busy status code. However this 503 status message is then sent to the end user
devices when the SIP/ISDN gateway sends back a 486 busy here status code.

Is there any way that Asterisk can be configured to pass on status codes
unchanged or at least to group certain status codes received from the SIP/ISDN
gateway into specific code that are sent to Asterisk?

Thanks.

Regards

Tony Friar