Network effects aren't a big deal when it comes to messaging. There was a time when people thought iPhone wouldn't be able to overcome Blackberry because everyone was on BBM. In the last couple decades we've seen people go from ICQ to AIM/Yahoo/MSN to Google Talk to Skype to Facebook Messenger to BBM to Whatsapp/iMessage/Instagram, with dozens of smaller options like Kik, Viber, Line, Signal, Telegram all hanging around. It doesn't take much to cause another shift in the space.