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Please contact your Carrier as VoiceMail is a carrier-specific feature --> Check your voicemail on iPhone - Apple Support

VoiceMail, whether it's visual voicemail or the traditional voicemail service, is a carrier-specific feature that depends on your cellular service provider. If you are experiencing any issues related to voicemail on your iPhone, it's essential to get in touch with your carrier for assistance. Here's how you can check your voicemail on an iPhone and what steps you should take if you encounter any problems:

Checking Voicemail on iPhone:

1. Visual Voicemail: On most iPhones and carriers that support visual voicemail, you can access your voicemail messages directly from the Phone app. Open the Phone app, and you should see a "Voicemail" tab at the bottom. Tap on it to access your voicemail messages in a visual and user-friendly interface.
2. Traditional Voicemail: If your carrier doesn't offer visual voicemail or if you prefer the traditional voicemail service, you can access your voicemail by dialing your carrier's voicemail number from your iPhone.

Troubleshooting Voicemail Issues:

1. Voicemail Not Working: If you are experiencing issues with accessing or receiving voicemail messages, it's essential to contact your carrier's customer support. They can help you troubleshoot the problem and ensure that your voicemail service is set up correctly.
2. eSIM Users: If your iPhone uses an eSIM, ensure that the eSIM is activated and set up correctly with your carrier. Any issues with the eSIM activation can affect voicemail functionality.
3. Network and Coverage: Sometimes, voicemail issues may be related to network coverage or signal strength. Check that your device has a stable cellular connection.

You may try some of these steps, please check after each step...

1. Sometimes, a simple restart can resolve temporary software glitches. Turn off your iPhone, wait for a few seconds, and then turn it back on.
   1. Restart the device. That's it.
   2. Still not solved --> Force restart iPhone - Apple Support
2. If the issue persists, you can try resetting all settings on your iPhone. This will not erase your data but will reset all personalized settings to their default values. Go to Settings > General > Transfer & Reset > Reset > Reset All Settings and confirm the action. Note that you will need to reconfigure your settings afterward. All settings—including network settings, the keyboard dictionary, the Home screen layout, location settings, privacy settings, and Apple Pay cards—are removed or reset to their defaults. No data or media are deleted.
   1. Reset All Settings: Return iPhone settings to their defaults - Apple Support:- Return iPhone settings to their defaults
   2. You can return settings to their defaults without erasing your content.
   3. If you want to save your settings, back up your iPhone before returning them to their defaults. For example, if you’re trying to solve a problem but returning settings to their defaults doesn’t help, you might want to restore your previous settings from a backup.
3. Make sure you have the latest updates installed.
   1. Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
   2. Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If none of the above steps resolve the issue, it is recommended to reach out to Apple Support or visit an authorized service center for further assistance. They can provide specific guidance based on your device model and iOS version.