What that sometimes means is that your SIM card has gotten loose (or gone bad) is no longer identifying your phone to the cell phone network. The network sees that a phone exists, but can’t tie it to an account.
The reason it says “emergency Calls Only” is that by law, all cell phones, whether on a contract or not, have to connect to 911.
Reasons for the SIM not working:
– your contract ended and you didn’t renew
– you are late on payments and they cut you off
– the local tower for your network is down
– the SIM card got loose.