That's only if you go with a contract though correct? There's nothing stopping you from going and buying a smartphone. Then you can use any plan you want.
You don't know how it works in the US. Two of the major carriers (Verizon and Sprint) use CDMA, so you can't just get a sim card and stick it into a smartphone and use any plan you want. Even if you buy a phone outright, no contract, they will still require you to have a data plan.
T-Mobile is less strict, and I believe you can use most smartphones with prepaid services on their network and choose whether you want data or not. AT&T is GSM as well but you can't just swap a sim card in - they will see you're on a smartphone and automatically add data to your account. And most people buy their phones with a subsidy because to buy a smartphone outright costs a lot.
Things do not work the same in every country.
EDIT: It's interesting because it has led to completely different markets for smartphones. In the US, there's no point in getting a lower-end smartphone since you pay the same anyway and if you use a subsidy (and face it, there's not much reason not to), the price difference is small. The prevalence of unlimited data has led people to use a ton of cell data, which is causing problems for the carriers. Even though many are now instituting caps, the caps are still pretty high for the average user. This is totally different from metered data where any amount you use, you pay for. Checking Wikipedia might only cost you a fraction of a cent, but it costs you, so people are more likely to seek out wifi hotspots. In the US, there's no reason to, since checking your email or doing other low-bandwidth activities have almost no effect on your bill or your total data usage in a month.
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