It took Flickr, one of the world’s largest photo-sharing sites, close to 2.5 years to reach 150 million photos, which could be uploaded from any computer and shot on any camera. But it took San Francisco-based start-up Instagram roughly just nine months to hit that same milestone–with just one mobile app, available only on iOS, writes Austin Carr for Fast Company.

Instagram, which lets users shoot photos with their iPhones and apply one-click vintage filters, is growing at a faster rate than Facebook, Twitter, and Foursquare were during the same stages. As for how Instagram will turn its initial success into a sustainable business model, co-founder Kevin Systrom says it’s too early to know and he’s not sharing how the company might monetize the app.

What he does say is that the company will soon broaden its service, improve its mobile photography capabilities, and push toward making Instagram more known as a social network than merely a photo-sharing app.

Instagram has 7 million users who upload about 1.3 million photos each day, which is remarkable considering the company only has four employees, hasn’t spent money on marketing, and hasn’t released an Android app.

Read more at Fast Company ^[1].