How can I buy AT&T Smartphone without a data plan?

I had a Smartphone (AT & T Tilt) for 2 years. I paid for a text plan for the first month to get the phone in the contract. Then canceled the plan text, and have been with a single voice. But now I'm looking to upgrade my phone. One friend of mine told me that all phones from AT & T require a data plan. A lady in the store of AT & T told me I could not even use an unlocked phone. AT & T could detect that this was a smartphone and I require a data plan. I do not think this is correct. If I buy a phone, I can not see how AT & T can force me to something that does not need or want. Can anyone shine some light on this?

I have said exactly the same today in the shop of AT & T. I think it would be illegal to add just the data plan on your plan if you did not agree or sign up for that. Noone can make the changes to your plan without your consent.

I wonder if why not just buy the phone in retail somewhere, then just switch the phone you are currently using? That does not count as an update, and I've done this many times when I had to break the phone, and just switch to another phone that was out there.