Wireless carriers in the US offer unlimited data only on slower speeds - or they may throttle down from 4G to 1X speeds after 5GB is used, for example. Unlimited text, thankfully, is the norm.
Incidentally, I found out about the number of text messages my son was sending and receiving (you're charged for both) because the carrier had set up the plan wrongly and they were charging 1c per message. The bill had a charge for over $100, which is quite amazing. That translates to about one message every minute for every waking hour. We had a serious discussion after I saw that!