[Asterisk-Users] Custom SIP messages

[snacktime]

Two questions actually.

First, is there a way to trigger an action based on a particular SIP
message, such as an ACK response to an INVITE and a BYE message?

Secondly, if #1 is possible, is there a way to have it trigger a
custom SIP message to another SIP server?

Assuming this isn't possible, what would be the simplest way to create
this functionality?

I'm toying with the idea of using such a method to send call detail
information to a separate accounting server at a remote location.

Chris