I understand that you want to know how to get the Slingbox IP address when you are away from the Slingbox location.
You only need to launch the connection from www.slingbox.com, then select the "Support" tab. On this page you will be able to find the IP address provided by the router for your Slingbox. This is the same IP address that allows the connection from any remote location, even if you use any of the Mobile applications.
Hope this helps.