My iphone 4 on IOS 7 has had no service for a whole day and still has no service How can I fix it?

My iphone 4 on IOS 7 has had no service for a whole day and still has no service How can I fix it?

Take out your SIM card and put it back in again, see if that sets it straight. If not, take it to your carrier and tell them about the situation.