Either a bad or dirty card or a broken socket are the usual problems. Your carrier can check the card and replace it if necessary. (They normally won't charge you.) Or you can check it out - put the card in someone else's phone who uses the same carrier. If you get service, put it back in your phone. If it works, the card was dorty, if not it's your phone. If you don't gt service on their phone, the card is most likely bad. (They're pretty much the same as SD cards and, like SD cards, they go bad - some of them almost out of the box. My last phone wouldn't register when I bought it. Bad card right out of the box.)