So Facebook is again trying to become a bigger part of people's lives with free member to member calling in the USA. That means they're still not doing what Skype does, but this is today. What Facebook is doing is pretty much ICQ era presence and ICQ era voice calling. See the person online, connect and talk.
Maybe in the future you'll be able to call a brand, order a pizza, or arrange for flowers. Maybe you'll connect to your personal banker who is also on Facebook, but if the person isn't using an iPhone, isn't online, you're not talking.