People send more messages over chat apps than SMS, and it has phone carriers shaking in their boots. 

With chat apps overtaking SMS by sheer volume globally, "the cash cow is dying," says Neelie Kroes, Europe's digital chief for Informa analysts.  

According to an Informa report released Monday, 19 billion messages were sent over these apps worldwide in 2012, versus 17.6 SMS messages. The next two years could be even bleaker, with consumers sending 50 billion messages, versus 21 billion text messages. 

While the picture of who's using these apps remains hazy at best, a few have emerged as frontrunners. WhatsApp, BlackBerry Messenger, Viber, iMessage and KakaoTalk are among the most popular, according to Giga Om, although Facebook Messenger for Android (100-500 million installations) and China's TenCent (around 300 million users) are also leading the pack. 

[ht @sfiegerman]