Your iPhone typically responds quickly when you choose to end a call, but sometimes you can't disconnect. As essentially a mini-computer, your iPhone is susceptible to the occasional glitch, causing it to freeze and stop responding properly. This can happen for a variety of reasons, such as a newly-installed problematic app, out-of-date operating system or corrupted files.
Before you can narrow down the cause your problem, you must first regain control of your iPhone. Press the "Home" button to exit out of call mode. If the phone doesn't respond to this or any other key presses, perform a restart by pressing and holding the "Sleep/Wake" button until the red power off slider appears. Swipe it to the right to power down. Press the "Sleep/Wake" button again to power up.
Reset Your iPhone
Sometimes your iPhone freezes so completely that it will not respond to a restart and must be reset instead. This is the equivalent of a hard reboot on a computer, and should be performed only if the phone doesn't respond to normal power down attempts. Press and hold the "Sleep/Wake" and "Home" buttons at the same time for 10 seconds. When the Apple logo appears on the screen, release the buttons.
Troubleshoot the Cause
If your iPhone started acting up after the installation of a new app, that may be your culprit. Delete the app and see if your freezing and stuck call issues continue. Every running app consumes processing power, which can cause slow downs and operational problems in other areas. Close any unnecessary apps or programs to save both battery life and processing power. A shortage of storage space can also cause freezing issues, so regularly go through your phone and remove unused apps and games. Keep at least 2GB of space free to minimize operational issues.
Update or Restore iOS
Freezing issues in your iPhone can occur due to problems with your operating system, including outdated, corrupted or damaged files. If your various troubleshooting fails to unveil the cause of your issues, make sure your iPhone's iOS is up-to-date. You can check for updates wirelessly under your iPhone's Settings menu, or by connecting to your computer and opening iTunes. If all else fails, you can restore your phone to factory defaults. This will completely erase all personal data, so back up your phone first with iTunes or iCloud.
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