Hullo is a Windows based client that provides VOIP calls to North American numbers for free. You can call any landline, mobile or Hullo PC user for free unlike Skype which charges for SkypeOut (although Hullo probably will start charging once out of beta). You need to download and install a client on your desktop PC, add contacts and hit the call button. if the contact is a non Hullo user, it will dial the 10 digit number.