no service

or you need to get a new sim card from your carrier (which are normally free). Try that option first, if it doesn't work it could be other things, like the sim card reader in your device is not reading it correctly, the sim tray is loose and your phone cant get a good read on your sim card, you might need to do a network refresh which can be done in settings. If you get a new sim card and that still doesn't help fix the issue, I'd recommend taking it to your closest Apple store and having them look at it.

it needs a sim card to get cellular service, if it's sim locked to a carrier it needs a sim from that carrier or to be unlocked by that carrier