Can I share a data plan on at&t?

My mom and my sister both have a plan on at&t. My mom has some kind of gophone with a touchscreen and my sister has iphone 4s. I just got a samsung galaxy exhilarate and was wondering if I could share the data plan with my sister or if I need my own individual plan. I will not need the data because I use Wi-Fi and only need the phone for texting. Is there any possible way to have the smartphone on a data and text plan only?

I believe you can hotspot but you have to pay extra

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