Why does my iPhone 3G have no service?

Ok for some weird reason on Friday in the morning my phone had service but then in the afternoon after school was over it didn't have service. Also I have been asking my parents for an iPhone 5c since it came out and in the morning I had no present under the tree. Then when I came back from
School I had one. Is there a possibilty they got me a new phone? Or could it be just sim card problems?

You hit the "airplane mode" by accident. Turn that mode off

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