Back in Skype's early days, it was adding users so fast that it liked to boast that it was "the fastest growing, globally available communications tool in history." Well, by at least one measure (registered users 9 months after launch), mobile video chat service Tango is outpacing Skype. Tango now has 17 million registered users across both Apple and Android devices, only 9 months after it launched. By comparison, Skype celebrated 9 million users on its first birthday back in 2004. Today, Skype has more than 600 million registered users, so Tango still has a long way to go. But the company wants to reach 100 million users over the next year. (Don't we all?). If it does that, it will certainly earn the title of fastest growing communications tool.