Changing the settings on your smartphone may resolve the issue.
For details, please refer to the information below.
Mobile Data Settings
On the home screen, go to "Settings" [設定] → "Mobile Data" [モバイル通信] and make sure "Mobile data"[モバイルデータ通信] is turned on.
Please turn off "Mobile data" [モバイルデータ通信] once, then turn it on again and check if you can use mobile data.
Wi-Fi Settings
On the home screen, go to "Settings" [設定] → "Wi-Fi" → If "Wi-Fi" is on, turn it off and check if you can use mobile data.
Airplane Mode Settings
On the home screen, go to "Settings" [設定] → "Airplane Mode" [機内モード] and make sure that it is turned off.
Please try turning on "Airplane Mode" [機内モード] once, and then turning it off again, check if you can use mobile data and make calls.
Restarting the Device
There may be a temporary malfunction, so please turn off the power and then turn it back on (restart).
After that, please check if you can use mobile data and make calls.
Updating iOS
If there is a problem with the iOS software, updating it may allow you to connect to Wi-Fi.
If there is a newer version of iOS released, try updating the software.
Reset Network Settings
If you are still unable to connect to Wi-Fi even after restarting your iPhone and router, resetting your iPhone's network settings may solve the problem.
Mobile Data Settings
On the home screen, go to "Settings" [設定] → "Network & Internet" [ネットワークとインターネット] → "Mobile Network" [モバイルネットワーク] and make sure "Mobile Data" [モバイルデータ] is turned on.
Try switching off your "Mobile Data" [モバイルデータ], then turning it back on again, and check if you can use mobile data.
Wi-Fi Settings
On the home screen, go to "Network & Internet" [ネットワークとインターネット] → "Internet" [インターネット] → Wi-Fi. If Wi-Fi is turned on, turn it off, then check if you can use mobile data.
Airplane Mode Settings
On the Home screen, go to "Settings" [設定] → "Network & Internet" [ネットワークとインターネット] and make sure that "Airplane Mode" [機内モード] is turned off.
Try turning on Airplane Mode once, then turn it off again, and check if you can use mobile data and make calls.
Restarting the Device
There may be a temporary malfunction, so please turn off the power and then turn it back on (restart).
After that, please check if you can use mobile data and make calls.
Troubleshooting
Please check the Malfunction Detection.
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