[Users] Remote PSTN gateway

Hi there! I would like to implement the following scenario using OpenSER: - when a SIP client sends a request consisting of only a simple phone number (on the form +CC-AAA-NNNNNN, with or without plus sign, hyphens, possible spaces etc where C, A and N are simple numbers) OpenSER should route the request to another, remote SIP-proxy acting as a PSTN gateway. - either the same credentials should be used or preferebly credentials dependent on the domain name of the callee for all requests to the SIP-proxy - after the session with the remote proxy has been set up OpenSER either works as proxy between the client and the remote proxy, or better transfers the session to the client - all requests for a client not on the form of a phone number (i.e. with a fully qualified domain name should be routed to the correct location as decided by SRV-records etc. Is this possible? Any hints on how to accomplish this? Sincerely, Kris PS/Please note that I am new to OpenSER, SIP and SIP terminology...