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I've had an iPhone since the 3G with unlimited data and I've only gone over 2 GBs once and that was during last year's NCAA March Madness. The devices only destroy your data if you sit around and watch Netflix and tether all day. Standard browsing and watching a few videos will keep you under 2 GBs.

I dont tether or watch netflix. I listen to Pandora, Spotify, and Stitcher in the car. I get email from 4 addresses, I chat, I surf, I use facebook. I use my iPhone all the time, and maybe use 60 mins a month. I can't remember the last time I watched a video and tethering is another fee and has nothing to do with the unlimited data anyway.
 
I only used to use data for light browsing and email, which came to a total of 1GB down 150MB up in 3 years ( 2 with iphone 3G, 1 with iP4) so 200MB can easily be enough for a month depending on your requirements. I'm up to like 400-500 a month now since I stream Kerrang radio every day for about an hour.
 
I'll add my 2 cents....I have wifi at home and at work, never stream anything unless I'm on wifi and generally don't go over 100 mb/month. If I had an unlimited plan I'd probably use a lot more just because I could without worrying about it, but I never feel like I'm missing anything because of my 200 mb plan.
 
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