Some iPhone 4 owners have reported losing their cellular network connection on the device after removing and reinserting the phone's SIM card. Other users have experienced restricted network errors when they update the iOS operating system. If you receive an error on your device that your cellular network is restricted, first disable all of your network connections, then reset your network carrier to reacquire a connection with your cellular service.... Step 1 Power on your iPhone 4. The message “Insert Your SIM Card" displays if the SIM card is absent when the phone boots up. Step 2 Insert your SIM card, and then tap “OK.” Step 3 Tap the gear icon in the iPhone 4 springboard, and then tap “Phone.” Tap the “SIM PIN” option, and then tap the slider to disable the SIM PIN. Tap the “Phone” option, then the “Settings” option to return to the Settings menu. Step 4 Tap the “General” option in the Settings menu, and then tap “Network.” Slide the “Cellular Data” switch to the “Off” position. Tap the “Network” arrow, and then tap the “Settings” arrow to return to the Settings menu. Step 5 Tap the “General” option in the Settings menu, then tap “Network.” Slide the “Cellular Data” switch to the “Off” position. Tap the “Network” arrow, then tap the “Settings” arrow to return to the Settings menu. Step 6 Tap the “General” option, then tap “Date & Time.” Slide the “Set Automatically” switch to the “Off” position. Tap the “General” arrow, then tap “Settings” to return to the Settings menu. Step 7 Tap “Network Selection” and slide the “Automatic” slider to “Off.” Tap the “Settings” arrow to return to the Settings menu. Step 8 Tap the “Wi-Fi" option and slide the Wi-Fi slider to “Off." Tap “Settings” to return to the Settings screen. Step 9 Tap “Airplane Mode,” then tap the switch to turn it to “On.” Leave the phone in Airplane Mode for one minute. Step 10 Slide the “Airplane Mode” switch to the “Off” position. A message appears in the top navigation bar as the iPhone searches for service. Step 11 Tap the “General” option in the Settings menu and tap “Reset.” Tap “Reset Network Settings.” Tap the red “Reset Network Settings” option to confirm. The Apple logo is displayed as the phone’s network settings are reset. The iPhone springboard screen displays and the device searches for service. Your unrestricted network is detected. If your network is not detected within two minutes, proceed to the next step. Step 12 Tap the gear icon in the iPhone springboard, then tap “Network Selection.” Tap “Carrier,” then “Automatic” to turn the Automatic feature “Off,” if the feature is turned on. The device searches for and lists carriers in range. Step 13 Tap the entry for your carrier. For example, tap “Verizon Wireless” to manually configure your carrier as Verizon. The device connects to your carrier and you have an unrestricted connection. Things Needed Valid SIM card Warning Information provided in this piece applies to the iPhone 4. Instructions may vary slightly or significantly for other models of the iPhone.