My wife got the S3 three days ago. Everything fine until today, suddenly no service and a sim card issue. Customer service recommends taking to the store to replace the sim card. We take the back off and, lo and behold, the sim card is not seated, it is up about an eighth of an inch. Slide it back in with a fingernail and put the battery back in, and the problem is resolved. The phone was not dropped or jostled in any way to cause this issue.