Mobivox lets you make international phone calls from any phone ( I tried with my cell) for free and without having to create a new number for your international contacts. I'm currently using Rebtel that I found being the best solution so far but I'm about to switch to Mobivox. Why? Because, it's really free and doesn't require me to tell my friends to hang-up and call me back. The way Mobivox works is simple: you register online; enter/upload your contacts, even from Skype; call the local number; speak the name of your contacts and boom! Mobivox is like a calling card (you can also type in the number of the person you want to call), but the call itself is 100% free if your contact is also a Mobivox users. Can't beat that!
Mobivox's interview after the jump.