As an AT&T data point, I pay $162 a month for 3 iPhones on a 25 Gig data family share plan, which I think is still too expensive, but not that bad.
Then I switched to Ting 6 months ago. The highest bill I've had since: $42 If I have a month where I use 10GB, my bill might reach $200 for that one month. I still come out WAY ahead in the long run.