You can monitor the current SIP activity. The tables are updated when you select the page or reload it.
Here the currently active sessions are listed.

The SIP address of the called user.
The name and SIP address of the calling user.
Each SIP session has a unique ID, which is shown here.
Here the currently registered users are listed.

The SIP address of the registered user. The address looks like name@domain, where name is a user name or a telephone number, and domain is a domain name or the IP address of the SIP registrar (the firewall).
The IP address of the computer from which the user registered.
If the VoIP Survival module is installed, aliases for this user is shown here. The aliases shown are the ones configured for the user on the main server.