If im not mistaken it means your data service is off. If you try to make a phone call or use the internet it would most likely prompt you to turn your radio back on.
Can happen when the battery is low as well. Manage connections to put the check mark in the box by mobile network or try to make a call will/should get it back. If its a low battery it wont work until its charged up a bit (around 20 percent)
Yes this is what it means. It will prompt you to turn it on, or you can go into the manage connections icon and place a check in the network box. Also as stated above charge your every night.