Why won't my iPhone 4S activate?

So I have this white iPhone 4S that used to belog to my brother but its mine now and it's AT&T unlocked and every time I try to activate it i get this:
Your iPhone could not be activated because the activation server is temporarily unavailable. Try connecting it to iTunes to activate it, or try again in a couple of minutes.
I've been trying to activate for like 3 days and it still wouldn't work. Should I just go to the apple store and have them activate it?

Are you trying to use it with a different carrier other then ATT or T-MOBILE? If so you can't use it. The only networks an ATT iphone 4s unlocked will work with is those two because of the different bandwiths in other companys and those two are both GSM carriers, SPRINT and VERIZON are CDMA carrier and aren't sim card based if not you can always call ATT or T-MOBILE

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