It took about 75 years for the telephone to connect 50 million users
The radio hit this goal in 38 years.
It took 13 years until 50 million people were sitting in front of their television screens in their home.
The Internet reached this milestone in 4 years.
Facebook: 3 years.
It took the iPhone 3 months to get into 50 million pockets.
Angry Birds: 35 days