I have a local kamailio+rtpproxy under NAT listening on multiple local interfaces (vlans) which works fluenty for all local user indipendently and engages rtpproxy correctly. 

I have another working kamailio+rtpproxy which is accessible from everywhere at a public address and I would like to route to it some specific calls from the local server. 

So, in the local kamailio configuration file I defined WITH_PSTN (all the necessary option) and INVITE/OK/BYE messages are going correctly to the destination. The problem is that I have no audio on both ways.

After some packet sniffing, I tried killing local rtpproxy process and now calls to PSTN have also audio both ways.

From these tests, if my configuration is correct, when routing the call to PSTN gateway I should disable the local rtpproxy, and I'm in doubt about how I can do this. 

Could you help me? Should I change NAT flags in the PSTN route?

Thanks