Do I have to get a data plan if I buy an iPhone?

I want to get an iPhone but I don't want to get a data plan until later. I was just wondering if you HAVE to get a data plan in order to have an iPhone. One of my friends says you don't. She doesn't have a data plan. And my sister got her friend's old iPhone and just put her old SIM card into it and doesn't have a data plan. Although, some people say you need one. I'm just so confused. I go to AT&T… Would they force me to get one?

All carriers require a data plan if you setup phone calling. Maybe you could check other carriers

Have to? Force you? Yeah. No carrier on earth will sell you one without a data piece as part of a plan. That's how they make truck loads of cash is data; even the Paygo cards with monthly plans. So do what your sister did then. Why? If you can work around it, you can use the phone that way but can only use internet and apps when on Wi-Fi-nothing else. Best luck.