Bill Gates has said that Facebook and Google weren't the only companies looking to buy WhatsApp, Microsoft was also willing to buy the messaging app. Microsoft's founder said the company was willing to buy mobile-messaging startup WhatsApp, which social network site Facebook recently bought for a whopping $19 billion. While he acknowledged that WhatsApp is a valuable acquisition, he wasn't sure if it was worth the price Facebook paid for it. "Microsoft would have been willing to buy it, too. I don't know for $19bn, but the company's extremely valuable," Gates told Rolling Stone in the wide-ranging interview. "I think [Zuckerberg's] aggressiveness is wise -- although the price is higher than I would have expected. It shows that user bases are extremely valuable," said Gates. Mark Zuckerberg has defended the price his company paid for WhatsApp saying that the messaging app is well on its way to connecting a billion people. The acquisition, which is Facebook's biggest purchase, also signals the social network's aggressive drive from the desktop to mobile. Gates called Zuckerberg more of a product manager than he was at Microsoft, where he instead started off with software architecture. Read the rest of the Rolling Stone interview here.