Connection/Network Issues

I keep getting the error message, "currently unable to send your text message. It will be sent when service becomes available" when I try and send a text. And when I try and listen to a voicemail it says, "your phone's not registered on a network, so you can only make emergency calls". If I try and open an email it says "no connection". It has been working fine and now all the sudden I have no service or connection??