iPhone 4 Activation Error

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Hello

I am having a hard time figuring out this iphone 4 that I got as a present a few weeks back. It's from the U.S. and from what I can gather it's from AT&T.

The problem is that when I insert a sim card its states that it is an invalid sim. When I remove it does not let me pass the screen after wifi stating that "Activation request could not be completed. If the problem persists, please contact customer care". When I try to plug it in and use iTunes, it gives me "We are unable to continue with your activation at this time. Please try again later, or contact customer care." I cannot check firmware nor do I know what ios is on it. Im new to iPhones so I really dont know what to do. Order a factory unlock from ebay, use ultrasnow or what. I wanted to inquire first on what are my options?

Please let me know if I am asking in the wrong section, and redirect me to the proper section. I have surfed the web with allot of solution, but I really don't know which would apply to my problem. Sorry for my ignorance, and hope you can help me.

Thank you in advance.