Questions about USA and buying Mobile Phones!!! Please Help

[flyduffer]

I'm from Europe, but now I'm in USA for 50 more days. I really want to have the new iphone 3g s, but i have some questions for anyone who knows anything! So please help.
First, i want to buy iphone with contract for 2 years with at&t for 199 and i have to pay Early Termination Fee of 175$ if i cancel my contract after 35-45 days for example. Today I asked in a store RadioShack, and the seller told me, that i must pay extra 200$ for the device, if i cancel the contract before 90 days of it. So what do you think about this, do you know anything and whats the deal with other smartphones for example also with other carriers such T-mobile or Verizone, they also have Termination fee, but do day have extra taxes for devices with contract.
If anyone knows and answers, i'll be very thankful.
Thanks a lot, and excuse me of my terrible English