I remember paying metered data that cost around 0.005 cent per kb around 2006 (forgot the actual number but I'm pretty sure it's around that much). Having "unlimited" data is indeed revolutionary.
AT&T offered unlimited internet plans pre-iPhone. I had an unlimited 3G internet plan pre-iPhone. It wasn't intended for PDAs/smartphones at the time but it seemed like they never bothered to check IMEI's for devices they did not sell. I forget the exact price but it was cheaper on the family plan than the unlimited iPhone data plan.
That was a revolution. Before that, yes, you could run up a massive phone bill.
[1] https://www.apple.com/newsroom/2007/06/26AT-T-and-Apple-Anno...