[Kamailio-Users] sending calls to voip provider

Hi, I am with openser about my first 40 hours. So far i managed to install 3.0. Was able to make calls between registered phones. Enabled accounting, etc. Looks i have control ;) Now i have a very simple question. I want to send calls for land lines via voip provider, sipdiscount.com in my case. I want to enable so registered client agent can send invite to that server, but it should re authenticate somehow. I was looking for proxy_authorize www_authorize but it looks like it authenticate my phones only. I was trying rewrite rewritehostport, but of course was getting authentications errors. Is there any manual, previous discussion on this topic? Thank you.