Why doesn't my iphone have a signal, and all other mobile phones can?

Signal or operator problems, sometimes in some places with poor signal, will encounter such problems, the call will fail and need to redial. This situation is generally caused by the current bad signal. Just redial in another place.

Cell phone crashed, try to turn it off and restart.

The SIM card is not inserted correctly. You can try inserting the mobile phone card again. You can pick up the card by using the card pick-up pin or other similar items that came with the iPhone.

Hardware failure, it is recommended to go to the local Apple for authorized after-sales inspection.

It may be that the mobile phone has entered flight mode, and when it is turned on, it will prompt the words "Searching ...", indicating that it is searching for mobile network signals.