[Serusers] Domain and To header fields

Hi List, I have a multi domain ser setup with the domain module operating, and I need to check whether the TO header field contains a local domain or not. Can this be done with is_domain_local()? If yes how? Or do i need to write a new function based on is_from_local() to achieve such a goal. The Problem is that there is no possiblity to distinguish between our user calling 012345(a)iptel.org (Remote SIP desination) or 012345(a)domain.com (PSTN target) after (!) the initial INVITE, especially with loose routing. This is important because Request-URIs to the PSTN have to be transformed (add f.e. +49), but requests to other sip destinations have to not be touched. Thanks for your input, regards, Martin