Trying to activate my at&t gsm Iphone into straight talk services?

So I'm on the site where you activate the sim card and where your supposed to put the Serial Number/ MEID/ DEC in but above it says ''If you have an iPhone that you bought at Walmart or through our online store, please enter your MEID'' clearly i didn't buy the iphone threw walmart or their online store its obviously like i said an at&t gsm do I still enter the meid serial code will it still work?

You have to make sure you bought an AT&T straight talk sim card. Not a t-mobile one. If not the phone has to be unlocked.

Once you figure that out, just follow the steps it's gives