Speak softly and carry a big user base. It doesn't exactly roll off the tongue, but that might as well be the unofficial motto of WhatsApp. The cross-platform messaging service has been quietly spreading over the last couple of years, coming to every major mobile platform and gaining over 300 million active monthly users, according to AllThingsD. What's next for the quiet revolution? Voice communication.
Well, sort of - it's more like a short voicemail message, not a live two-way conversation.