If you've ever needed to call someone, yet have no idea how to get a hold of them, you'll understand the greatness of Vonage Mobile. In this modern day and age, the only way to get in touch with someone that isn't connected is by sending a Facebook message (because everyone has Facebook) and then praying that they check it, but often they don't.
Instead of this waiting game, the new Vonage Mobile app searches through your Facebook friends list and seeks out those who also have Vonage Mobile. There is no need to know any numbers, you just tap on the "Call Free" button and away you go! It would be kind of creepy if you were using the app to stalk ex-girlfriends and such, but the way you use the app is none of Vonage's, nor my, concern.
Vonage Mobile works over 3G and WiFi and supports phone calls and chat. It's also totally free... how nice.