If your iPhone is displaying "SOS Only" or "No Service" instead of showing your carrier's name and you're unable to make or receive calls or use cellular data, it could be due to several reasons. Here are some steps you can take to troubleshoot and potentially resolve the issue:
1. **Check Your Cellular Coverage**: Make sure you are in an area with cellular coverage. Sometimes, you may not have service due to being in a location with poor reception.
2. **Restart Your iPhone**: Try restarting your iPhone to refresh its network connections. Press and hold the power button until you see the slider to power off, then slide to power off. Wait a few seconds, then press and hold the power button again until the Apple logo appears.
3. **Check Airplane Mode**: Make sure Airplane Mode is turned off. If it's on, your iPhone won't be able to connect to cellular networks. You can toggle Airplane Mode on and off by opening the Control Center (swipe down from the top-right corner of the screen on iPhone X or later, or swipe up from the bottom of the screen on earlier iPhone models) and tapping the airplane icon.
4. **Check for Carrier Settings Update**: Sometimes, carrier settings updates are released to improve network connectivity. Go to Settings > General > About. If a carrier settings update is available, you'll see a prompt to update. Tap "Update" to install the carrier settings update.
5. **Check SIM Card**: Ensure that your SIM card is inserted properly and hasn't become dislodged. You may try removing the SIM card, then reinserting it securely. You might need a SIM card removal tool (a paperclip can work) to eject the SIM tray.
6. **Update iOS**: Make sure your iPhone is running the latest version of iOS. Updates often include bug fixes and improvements that can help resolve connectivity issues. Go to Settings > General > Software Update to check for and install any available updates.
7. **Reset Network Settings**: Resetting network settings can sometimes resolve connectivity issues. Note that this will reset Wi-Fi networks and passwords, cellular settings, VPN settings, and more. Go to Settings > General > Reset > Reset Network Settings. Enter your passcode if prompted, then confirm the reset.
8. **Contact Your Carrier**: If you've tried the above steps and still have "SOS Only" or "No Service" on your iPhone, contact your wireless carrier for further assistance. They can check for network outages in your area and troubleshoot any account or network-related issues.
If none of the above steps resolve the issue, there may be a hardware problem with your iPhone, and you may need to visit an Apple Store or authorized service provider for further diagnosis and repair.