Does data storage matter for iPhone?

I've never had a phone before, so I'm really new at this. I'm looking at Apple's website, and I click on something that lets me see plans from Verizon, At&t, and Sprint. They all charge money for data. My question is, does that matter? Should I go for the cheapest plan or what? The iPhone has gigabytes for data and storage and stuff, so why are the phone companies charging money for data? I'm so confused. I would appreciate any help.

The "data" mentioned in those plans means a different thing: it refers to mobile internet (3G etc). The carriers sell several kinds of plans: some are unlimited, i.e. There's no limit to how much you can use the mobile internet on your phone per month. Other kinds of plans have a limit, for instance 1 gigabyte or something more. All internet usage adds up: when you load a website, when you write an email, etc. Some data is sent on the network. Put all that together and you get how much of this kind of data you use per month.

What kind of plan you get depends on how much you think you might use it. If you only use it for web browsing, emails, facebook, things like that, something like 1 gigabyte should be enough. But if you think you will be, for instance, buying lots of music from iTunes on the data plan, you'll use up the 1 gigabyte very quickly.