Second Life will soon be available as an in the box, corporate solution for use behind company firewalls. Linden Lab is currently seeking closed beta testers at SecondLifeGrid.net and expects to have more details by the summer. And yes this will eventually be a paid product.
There are currently 9 alpha testers of this stand-alone version of the Second Life virtual world including IBM, Northrop Grumman, NMC, and more.