Having a Facebook account is no longer a requirement for sending Facebook messages. Users can now sign up for the Facebook Messenger mobile app by simply entering their cell phone number. “Messenger, which boasts 700 million users, is one of a suite of mobile apps that CEO Mark Zuckerberg is keen to grow to one billion users or more,” reports The Wall Street Journal. “Others include a second messaging app, WhatsApp, and photo-sharing app Instagram. WhatsApp has 800 million users, making it and Messenger the world’s two most-used messaging apps, according to market-research firm GlobalWebIndex.”