I remember when carriers upped the cost of text message from 15c to 25c per message. All four major carriers, iirc, changed their pricing within a month of one another. This is another service that costs them almost nothing. This is like one of those "trout in milk" evidence. I am positive they all got together and decided to raise rates but nobody went to prison for this collusion.
I mean I wouldn't have minded if they only charged for messages sent but they charged me for incoming messages as well. My friends had unlimited texting and as a poor college student I was trying to save money. I was so glad when grandcentral/google voice became available. I joined it and never looked back.