Can you unlock an iPhone 4 and not have a data plan with AT&T?

I have several friends who have unlocked smartphones and they said they use them without a data plan, only talk and text. All of them have T-Mobile and I was wondering if I could do the same for an iPhone 4 or 4S and have a text/talk plan. I'm in a family plan and I usually get 2 year-contracts on AT&T. Is it possible?

Yes, You can unlock it at low price.