we have seen that CISCO gateways add "proprietary" SIP heade fields such as:
Is there a way to disable them to be written in SIP packets?
You can take a look at this document:
You should be on 12.4(20)T or later to try these features. It says this is a CUBE feature, but I've confirmed it on one of my CME boxes in the labs.
This feature allows for you to do SIP header modifications for outgoing SIP messages. This will allow you to remove headers as long as they are non-mandatory.