You can do it bro, I did it about two or three years back when i was working in sri lanka for my previous employer, i bridged fiber router and terminated ADSL connection on a juniper firewall, unfortunately we did not use the voice connection on that connection though, you can get details from current router, they use separate vlans for different traffic so i think your requirement is possible only thing is you have to make sure that to find there PABX IP, username and password before proceed
Which Software did you use?
