Straight Talk and "unlocked phones"?

I have straight talk service with the at&t side of the network so i have a sim card. I am new to straight talk so i dont know all about it yet. I am looking for a new phone but dont have tons of money to drop on one. I was looking at the wal mart website and found some "unlocked" phones that I like. can i use one of those phones with my straight talk if that phone requires a sim card? i have researched it and some say yes and some say no so idk what to believe. thanks.