i cant use my iphone 4s in my country with our sim

please i need apple or anybody to help me out, i keep getting the error message

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The SIM card inserted in this iPhone does not appear to be supported.

The SIM card that you currently have installed in this iPhone is from a carrier that is not supported under the activation policy that is currently assigned by the activation server. This is not a hardware issue with the iPhone. Please insert another SIM card from a supported carrier or request that this iPhone be unlocked by your carrier. Please contact Apple for more information.