I am having the same problem. I activated a new phone for my mom today. Transferred straight talk number. New phone same carrier. Phone worked yesterday into today up until now when it's saying invalid sim. Called tech support and he tried telling me to put the card in the ad slot lol. I uninserted the sim card and reinserted and rebooted. Still invalid sim card. Basically now have a $150 that was used for a day. How does it go from working to nothing?