Are there any ways to use the iPhone without data?

I used a sim to call and text only when I saw my friends using the Iphone with a sim cut. I also buy an iPhone4s(AT&T) and put my sim cut in the Iphone. I use it more than 2 months without any charging, but until yesterday when I saw a 4G thing on my iphone and I try to use the internet, and I can go to facebook, download apps from appstore… I share a line with my aunt, so I called her and asked, Did she turn activate my sim to use the data. She said, no. Then she check her att account, and she saw they charge $30 more in my line, but last 2 month, there are nothing charging. She called to AT&T and asked why. They said, my Iphone have a feature that can activate the sim to using data when I put my sim cut in. I just have a question why, If it's automatically, it definitely activate 2 months ago, not using more than 2 months and it's automatically turn it on.

Some people just told me if you unlocked your Iphone, so the AT&T won't know that you're using the iphone and won't add data in your sim.

I just want to make sure IS this right? Or Are there any other ways to use the iphone(AT&T) without data plans?

Sorry for a lot of error grammar because I just came to US almost 1 year.

I think

No. BTW, I think you must mean "sim card", not "sim cut".

You can turn of all cellular data in settings that will deactivate your data usage and you won't be able to access the internet or anything that requires data usage.