The Firebrick is a back to back user agent, and on OnSIP must be configured for OnSIP Trunking.

Before you configure the Firebrick, you must first create your account with OnSIP and make two minor modifications.

First, login to the OnSIP App as Adminand click on "Users" on the left side of the screen. With the user you create in OnSIP, make sure that under "Advanced" that "OnSIP Trunking" is enabled.

Secondly, under "Phone Settings" note your "Auth Username." Select your Auth Username and copy it to the clipboard or simply write it down. Next, choose "edit info" under your "SIP Address". Modify your username to be the same as your Auth Username (found under Phone Settings).

For example, if your SIP address was user@yourdomain.onsip.com and your Auth Username was "yourdomain_user", you would change your SIP address to be yourdomain_user@yourdomain.onsip.com. As soon as you hit "save changes", you should see both the Auth Username and Username to be identical in the "Phone Settings". If they are not identical, modify the SIP address again to correct any issues.

In the Firebrick you would then use your Username (the same as your Auth Username now) as the From username in the Firebrick configuration screen.