Will an Iphone work with consumer cellular?

I'm going to buy an iphone 4s from somebody off of craigslist. It is an unlocked iphone that was previously used on at&t, and I was wondering if it would work on my plan for consumer cellular. I plan to just insert my sim card into the phone, and have it work. Will that be the case?

Added (1). If it's not the case, please explain how i will ave to do it. Also, if I can't, tell me why.

Mm yes

I don't know.