I feel sorry for people who get smartphones and think they only need limited data.
What the hell do you want a smartphone for? The big pretty screen?
I have an Evo 4G with a Ting plan and only 100MB of data/month. I'm 20 days into the plan and I've only used 12MB so far.
Not everyone streams 10 gigs a month on Netflix or insane amounts of music on the go. I stay on Wifi as much as I can, and keep my music locally, along with maps. I use data mostly for directions and when I really need it, not to check Facebook every 30 seconds. For my habits 100 megs of data is just fine.
As for what I use a smartphone for? I use it as a camera, a phone, a GPS device, a tuner for my bass, a metronome, a note-taker, a flashlight, a music recorder, a web browser, an MP3 player, an eBook reader (not ideal compared to my Nexus 7, but it works), and much more. You don't need data for most of those functions, and you don't need a huge data plan to really appreciate a smartphone. My previous phone (a cheap texting slider) could do none of those tasks well.
And if you do use 10 gigs of data a month, great. Go use T-mobile or Sprint then, and be happy. Ting isn't meant for you.