I love WhatsApp. I use it daily, especially to stay in touch with friends in Europe and elsewhere to avoid the costs of SMS. Sure, I can use GoogleVoice, but if those across the water don't have a US based GoogleVoice number it means an international SMS. Whatsapp helps me avoid that.
Recently rumors of a Google possibly making a purchase of Whatsapp made the rounds. And maybe there was some truth to it. Companies like Google always talk to smaller businesses about partnership or acquisition. Sometimes the negotitiations move along to a point where price is on the table, but often what Google and others like them are doing is looking under the hood to see if what's there fits into their long term strategy.
Candidly, the best buyer right now in Silicon Valley is Yahoo for WhatsApp, not the also rumored Facebook. The reason is simply this. Yahoo has basically moved in the direction of the mobile web, while Google is all about the browsable web. The fit between Yahoo and Whatsapp is likely better, as the Whatsapp team could likely be longer term players inside a new Yahoo and shape direction, while at Google it's all about Tim, Larry and Sergey and always will be for a long time. But at Yahoo, the opportunity has become more of a greenfield play.
But while all this is going on, and it goes on all the time, the best thing for WhatsApp to be doing is to keep driving user growth and to keep signing up mobile operators because in the end, those two metrics along with user retention and usage stats will be how the company is ultimately valued by whichever buyer pays the price.