Here’s the dirty secret about text messages. It costs a wireless carrier close to nothing to send and receive them — even though they charge about $10 a month for 500 to 1,000 texts.

Now, a new crop of messaging apps — including one recently bought by Facebook — are threatening the wireless industry’s cash cow. GroupMe and Beluga, bought by Facebook earlier this week, is among several free group messaging services that allows users to send texts to contact lists, Twitter followers and Facebook friends through a smartphone application. Fast Society also allows users to customize groups for messages and provides conference calls.

Text messaging costs next to nothing for the carriers, yet consumers are forced into expensive packages costing them $10 to $20 a month.

As Cecilia Kang notes, that all could change with success of apps like Beluga and GroupMe.

Their approaches could be disruptive enough to actual force the carriers to change their ways — or at least to find new ways to wring cash out of customers.