[SR-Users] Network Architecture Question

Hi, I am just getting started with Kamailio and have been following the book "Building Telephony Systems with OpenSER" by Flavio E. Goncalves. The book describes an architecture with a SIP Proxy handling registrations and handing calls to a PSTN Gateway. I now have a basic test network running where calls are routed via the SIP Proxy (Kamailio) to a third party PSTN Gateway. I feel that a better design would be to implement my own PSTN Gateway using Kamailio. This single gateway would then handle all third party PSTN gateways. Thus one Kamailio server would be facing my clients while another would be facing my suppliers. Is this a sensible architecture and are there any sample configurations for Kamailio performing this role? Thanks Rob Watkin