[Serusers] Advice needed

Hello, I'd like ask for advice on what is in your opinion the best solution in the following scenario. I have a bunch of sip servers (asterisk boxes as my users need pbx functionality) that can make sip call to each other and my PSTN gateway. Now I want to purchase PSTN terminitaion in several different markets (and probably more in the future). All those terminations will require authentication. I want all my boxes when they see non-local call to send it to a central routing server that would determine where this call should be sent and authenticate to the appropriate provider so that I don't have to configure all credentials on all asterisk boxes. Also I want it not to deal with the media at all. All media streams should go directly from asterisk box to the PSTN termination provider. So basically it should be central SIP router that is able to authenticate calls if neccessary. I thought I could do it with SER and its UAC module, but it appears UAC module doesn't work and probably won't work (see my previous post in this list about UAC backport to 0.9.0). Also I don't want to use asterisk in this place as asterisk always wants to stay in media path and I'd really like to avoid of getting into hassle with re-invites. So the question is what are my options and what you would advice as a solution. Are there any software out there that can do it (preferably open-source, of course) or what else you could suggest to do to get desired results. Thanks a lot, -- See you later, Michael