After cleaning, reinsert the SIM, power on the device, and test voice calls. This simple maintenance step restores service when the phone previously showed "Invalid SIM" or "No Service" messages. ## Restart and Toggle Airplane Mode A full restart clears temporary software glitches that prevent the phone from reading the SIM or connecting to the carrier network. Hold the power button, select Restart (or Power Off then Power On), and wait for the device to fully boot. Once online, open Settings, enable Airplane Mode for 15–30 seconds, then disable it. This forces the phone to re-register with nearby cell towers and often restores voice service without further action. If the issue persists after restart, check for carrier settings updates. On most phones, go to Settings > General > About (or similar path depending on the operating system) and allow any available carrier update to install. These updates contain network configuration files essential for voice calling. ## Test the SIM in Another Compatible Device Insert the same SIM into a different unlocked phone that supports your carrier’s network bands. If the second device detects the SIM and places calls successfully, the original phone likely has a hardware fault with its SIM reader or antenna. If the second device also fails, the SIM card itself may be damaged or deactivated.
When testing, ensure the secondary phone is compatible with your carrier’s technology (for example, GSM or CDMA support where still relevant) and that it is not locked to another provider. Successful testing isolates the problem and guides whether to replace the SIM or repair the original handset. ## Verify Account Status and Network Coverage Log into your carrier’s account portal or app using a computer or another device to confirm the line is active and not suspended for non-payment or other reasons. Check for any outage notifications in your area through the carrier’s status page or official social channels. Temporary network congestion or maintenance can block voice service even when data works. If coverage maps show strong signal where you stand yet the phone displays no bars, toggle between available network modes in Settings (for example, 5G Auto, LTE, or 3G). Some older SIMs or plans require manual selection of the preferred network type to restore voice calling. ## Update Device Software and Reset Network Settings Outdated operating system versions can conflict with current carrier protocols. Connect to Wi-Fi, open Settings, and install any pending system updates. After updating, perform a network settings reset: on most devices this is found under Settings > System > Reset options > Reset Wi-Fi, mobile & Bluetooth (wording varies). This clears corrupted APN or cellular configurations without erasing personal data.
After the reset, the phone will reboot and re-download carrier settings. Re-enter any custom APN details only if your carrier specifically requires them for voice service. Test calls immediately afterward. ## Contact Your Carrier for Advanced Support If the above steps fail, reach out to your carrier’s technical support. Provide the IMEI of the device (dial *#06# to display it), the SIM ICCID number printed on the card, and a clear description of the error messages. Carriers can remotely provision the SIM, push updated profiles, or issue a free replacement SIM that arrives by mail. When speaking with support, ask them to confirm that voice service is provisioned on the account and that no network-side blocks exist. Request a manual network refresh if available. In cases of persistent hardware issues, the carrier may authorize a device diagnostic or warranty claim. ## Additional Checks for Persistent Voice Errors Ensure Wi-Fi Calling is disabled temporarily during testing, as it can mask or interfere with cellular voice registration. Confirm that Do Not Disturb, call blocking, or third-party apps are not silencing incoming calls. For dual-SIM phones, verify the correct SIM is assigned as the default for voice calls in Settings.
If the phone shows full signal but calls fail with “Call Failed” or “Not Registered on Network,” remove any case that might obstruct the antenna and test outdoors or near a window. Extreme temperatures can also temporarily disable the SIM reader; allow the device to return to room temperature before retrying. Following these steps systematically resolves the majority of SIM card detection failures and carrier voice service errors. Start with physical inspection and cleaning, progress through software resets, and escalate to carrier support only when hardware or account issues remain.
