Do I need a data plan?

I'm interested in buying an unlocked Samsung GT-S5620 Monte, but I don't know if my SIM card will work in it. Is it considered a "smart" phone? I bought an unlocked Samsung GT-S5230 a few months ago and my SIM card works perfectly in it, but I heard that you absolutely NEED a data plan if you want to use a smartphone, even if it's unlocked. I DON'T have a data plan, so that's why I was wondering if the Samsung Monte is considered a smart phone, and if my SIM card would work in it even thought I don't have a data plan of any sort. Any help would be appreciated...