I have got trixbox system with two interfaces LAN and internet. It connected to two servers via internet (Kiev and Donetsk) + 2 portech gateways.
My sip_nat.conf:
bindaddr = 10.10.20.9
If I call to somebodies cell number through that server I can hear and the other side can hear me. But if I call to somebodies cell number from the phone connected to Kiev the other side cannot here me, but I can hear him.
your setup is not clear to me: what do you mean “connected to two servers”? do you mean it has SIP or IAX trunks to two different servers? If so, are these connected using the two different NICs? Do you have the routing set up correctly? When one works and the other does not it sounds like you possibly have a routing problem. Even if you bind to all addresses, you only have one default gateway which means the other route(s) have to be defined as static routes…