If your iPhone 17 Pro shows a "Not Registered on Network" error or displays an invalid IMEI, you won't be able to make calls, send texts, or use mobile data. The IMEI is a unique 15-digit number that identifies your phone to your carrier. When this identifier becomes corrupted or unreadable, your device can't properly connect to cell towers.
You can check your IMEI by opening the Phone app and entering *#06#. If you see "0" or an incorrect number instead of your proper 15-digit IMEI, your iPhone 17 Pro needs troubleshooting. Before considering complex repairs, work through these steps in order. Many common network errors can be resolved without ever touching the IMEI directly.
Restart Your iPhone 17 Pro
Always start with a simple restart. This clears temporary software glitches and forces your phone to go through a fresh network registration process when it powers back on. To restart, go to Settings > General > Shut Down, then turn it back on after 30 seconds. For a more thorough refresh, you can force restart your iPhone 17 Pro by quickly pressing and releasing the Volume Up button, quickly pressing and releasing the Volume Down button, then pressing and holding the Side button until you see the Apple logo.
Toggle Airplane Mode
Switching Airplane Mode on and off resets your cellular radio. Open Control Center by swiping down from the top-right corner of the screen. Tap the airplane icon to enable it, wait 15 seconds, then tap it again to disable it. This forces your phone to re-establish a connection with your carrier's network without a full reboot.
Reinsert Your SIM Card
A SIM card that isn't seated properly can cause registration failures. Turn off your iPhone 17 Pro. Use a SIM eject tool or a paperclip to gently press into the small hole on the SIM tray on the left side of the device. Remove the tray, take out the SIM card, and inspect it for damage or dust. Blow gently on the card and the tray slot, then carefully reinsert everything. Power your phone back on and check for a signal.
Verify Your Carrier Account Status
The issue might be with your service, not your phone. An unpaid bill, expired prepaid plan, or account suspension will prevent network registration. Use another phone to call your carrier's customer service or check your account status via their website or app. Confirm your line is active and in good standing before proceeding with more technical fixes.
Reset Network Settings on Your iPhone
This clears all saved cellular network configurations, Wi-Fi passwords, and Bluetooth pairings. It can resolve corrupted settings blocking your connection. Go to Settings > General > Transfer or Reset iPhone > Reset. Tap "Reset Network Settings." You'll need to enter your passcode. Your iPhone 17 Pro will restart and you'll need to reconnect to Wi-Fi networks afterward.
Update iOS Software
Apple releases iOS updates that often include fixes for connectivity bugs. An outdated version of iOS may have a known issue that's already been patched. Connect to Wi-Fi, then go to Settings > General > Software Update. If an update for iOS 26 is available, download and install it. Let the update complete and see if your network connection is restored.
Try a Different SIM Card
Your SIM card could be faulty. Borrow a known-working SIM card from a friend or family member (or use a spare if you have one) and insert it into your iPhone. If the new SIM card connects to the network without issue, your original SIM is likely damaged. Contact your carrier to request a replacement. If the borrowed SIM also fails, the problem is with your phone's hardware or software.
Erase All Content and Settings
This factory reset is a last resort, as it will delete all data and settings from your device. Ensure you have a recent iCloud or computer backup first. Go to Settings > General > Transfer or Reset iPhone > Erase All Content and Settings. Follow the prompts to completely wipe the phone. After it restarts, set it up as new (don't restore from backup yet) and see if the network error is gone. If the problem persists after a clean setup, there may be a hardware issue with the cellular modem in your iPhone 17 Pro, and you should contact Apple Support.