This is the server where you send all data to when registering your SIP line and conducting phone calls.
Use the specified server as the outbound server - use the SIP proxy server as the outbound server.
Use a different outbound server - specify another outbound server.
Do not use an outbound server - select this option to disable the outbound proxy. This will essentially disable your SIP line, as you will not be able to send data anywhere on a LAN or the Internet.
Authentication User Name
This option allows a different username from the Sip Number (or User Name) used for the Sip line to be used to authenticate the connection to the Sip server.
Use the default User ID for authentication - use the Sip Number (or User Name) defined for the default Sip line for server authentication.
Use a different username just for authentication - specify another username to authenticate the connection to the Sip server.
Click "Restore Defaults" if you want to rollback any changes that you have made to the Advanced Line Settings dialog.