In just five years, WhatsApp grew into a smartphone messaging service used by nearly a half-billion people.

The Silicon Valley-based startup founded by former Yahoo employees Brian Acton and Jan Koum in 2009 took its name from a play on the phrase “What’s Up,” according to its website.

The stated mission was to build a better alternative to traditional SMS messaging in a world where smartphones were clearly becoming ubiquitous.

The founders jokingly described themselves at the website as “two guys who spent combined 20 years doing geeky stuff at Yahoo! Inc.”

WhatsApp Messenger is a platform for sending images, video, audio, or text messages for free over the Internet using data connections of smartphones.

The application is free, but after using it for a year, there is an annual subscription fee of 99 cents.

“We feel that this model will allow us to become the communications service of the 21st century, and provide you the best way to stay in touch with your friends and family with no ads getting in the way,” the startup said in a blog post discussing pricing.

WhatsApp is reported to have more than 450 million users and said to handle more than 10 billion messages daily.