On at&t, does the bill per month go anymore higher once you get a smartphone?

I heard from many people on different services that they have a regular phone, and the bill is what it is with Unlimited data plan and text messaging. Once they get a smartphone, like an Android, the bill goes up to over 100 dollars, maybe even 200. I went into Best Buy and they told me that it doesn't go up at all unless you have an Evo or something which is 10 dollars extra. What's the truth?On at%26amp;t, does the bill per month go anymore higher once you get a smartphone?
What? The bill is whatever you sign up for. So if you sign up for an Evo 4G on a $99 a month contract, with unlimited everything, you will be billed $99 unless you start making calls and texts and data usage outside what your plan covers such as international calls.On at%26amp;t, does the bill per month go anymore higher once you get a smartphone?
Yes because with smart phones you have to get a data package, but how much it is depends on the service.