Try removing the SIM card after turning off the phone and reinsert. Turn it on and if still get same error, the phone is defective.
We recently went with Cingular and today while on a ride my cell phone got a little "weird." It keeps telling me to insert card and I can't even get to the menu or anything. The phone was in my side pocket of my motorcycle jacket and since it's a flip phone and hubby isn't leaning on me, I don't think anything got pressed by accident???

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