i am sad

i got iphone 4 from denmark gifted from a ´friend but he have been honest with me that the iphone 4 he found it in bus when he was travelling the the around the city, he decided to offer me the phone,but the phone could not work in denmark they told me that the the onwner of the phone listed his phone to a black list so no one can use it any more. but when i was in portugal i can able to use it but now i am in sweeden i cant use it anymore. is any one can help me about it.? i would appreciate your regards.