yes Dear,
the point is that there was an old setup with the VOIP-SP as below:
192.168.1.1 MIP(x.x.x.34) with SIP ports allowed. (to initiate a call)
10.10.10.1 MIP(x.x.x.35) with RTP UDP ports allowed. ( to exchange the actual call voice packets)
the new setup is to have only one private IP that needs to be NATed and will handle SIP and RTP UDP packets.
but the VOIP-SP have only the old configurations and its very hard to inform them to change the configuration to send SIP and RTP on one NATed IP (will take much time).
this is why im trying to point both public IPs to the same private IP so all the traffic send to x.x.x.34 and x.x.x.35 will reach 192.168.1.1, and all outbound traffic to use x.x.x.34