Do I have to get a plan as soon as I buy an iPhone 5?

I don't know if this will sound stupid, but I want to buy an iPhone 5 in the US from at&t to then unlock it in another country (where I will use it). But, do I have to buy a plan first in order for them to give me the iphone? I ask this because when I looked in apple.com it wouldn't let me checkout without choosing a plan. Would I have to choose a plan and buy it, then unlock it?
Can I go to an at&t store up front, buy the iphone there, then ask them to unlock it for me?(at an additional cost)
P.S.: I know I can buy an unlocked one but it is much more expensive like 400 more dollars and you can do it through different means with at&t, so please don't suggest that.

Let me correct your statement. You can buy the iPhone there, but they won't unlock it for you unless you pay for it up front (in other words, you have no choice but to buy the whole thing unlocked).So the method that you don't want suggested is the only way to get the iPhone completely unlocked to use in your country. Hope this helped.

You would have to buy it elsewhere, if you buy through at&t you are buying it on contract.

If you buy the phone from AT&T, it will cost you $199 + $85 monthly fee (minimum) for first month + $36 activation fee + $325 as Early Termination Fee + TAX (depending from state to state). That almost comes to $650 with taxes. So you're spending the same amount as the unlocked one. What you can do is get a Verizon iPhone 5 which comes unlocked for any SIM from outside Apple or Verizon and you can get the phone for much less. You can mail this person (arghyle@rocketmail.com) who can help you with the iPhone 5.