'm not sure how they plan to get it as widespread as Skype. I'm sure you can't call to it using Skype, and do they plan to give out numbers and really cheap Skype2Phone calls for mobiles and landlines? Do they plan to get Facebook and all other services to use it? It's not only some client or server software that you need, you also need Skype's services and those landline phone calls and integration, and userbase.
And the social problem of non-free software? People do not care. They never have, they never will. I doubt Stallman cares about every little detail about things he uses but isn't that interested in. When he is cooking his tv dinner, he just wants a microwave that works. When Stallman goes to his weekly pony riding classes, he just wants a pony that works without going into every mundane detail. Some little girl could think that Stallman is evil because he doesn't raise, feed and have the pony at his home as part of the family, but while Stallman doesn't have time to raise a pony, he wants to ride one. That's when you take what's easy for you without going in to details.
Look, the cause is stupid people. But you cannot fix stupid people. So what to do?