I have a Verizon Kindle Fire HDX that is added to my data plan. For about the last month, when the network option is on, it doesn't work. In the status bar it says "invalid sim". I don't know if this is a Verizon issue or a Kindle issue. I don't understand since there is not a sim card that I installed. When I get it, I will turn off the network and turn it back on. Sometimes this works for an extended time and sometimes it works for a minute or so. Anyone else have this issue?