The problem of Voicemail not working on iPhone is usually caused due to incorrect Voicemail settings and also due to your cellular service providers network going through problems.
In addition to above, Voicemail problems on iPhone can also be caused by software related issues, corrupted Network Settings and other reasons.
Voicemail Not Working on iPhone
If Voicemail is not working on your iPhone, you should be able to fix the problem using the following troubleshooting steps.
1. Check Voicemail Setup
Make sure that voicemail is set up and switched on your device.
1. Open Settings > scroll down and tap on Phone.
2. On the next screen, make sure that you can see Change Voicemail Password option.
If you do not see the option to change Voicemail Password, you need to setup Voicemail and Password by tapping on the Voicemail tab in bottom menu.
2. Force-close the Phone App
The problem might be due to the Phone App on your iPhone being stuck or going through problems. This can be fixed by force-closing the Phone App.
1. Swipe-up from bottom of the screen and this will bring up Icons for all open Apps on your device.
2. Swipe-left or right, until you find the Phone App and swipe it up to close the App.
After this, re-launch the Phone App and see if Voicemail is now working on your iPhone.
3. Enable/Disable Cellular Service
Momentarily disabling the Cellular service on your iPhone and reconnecting it back again is known to help in fixing this problem.
1. Open Settings > tap on Cellular.
2. On the next screen, move the toggle next to Cellular Data to OFF position.
3. Wait for 30 seconds > enable Cellular Data by moving the toggle to ON position.
4. Restart iPhone
The problem might be due to a stuck apps or processes, preventing the Voicemail from working properly on your iPhone.
1. Go to Settings > General > scroll down to bottom and tap on Shut Down.
2. On the next screen, use the Slider to Power OFF iPhone.
3. Allow iPhone to completely Shut Down > Wait for 60 seconds and Restart your device.
5. Check Call Forwarding
Make sure that iPhone is not forwarding unattended calls to another phone number, instead of diverting them to voicemail.
1. Go to Settings > Phone > Call Forwarding.
2. On the next screen, make sure Call Forwarding is set to OFF position.
Once Call Forwarding is disabled, the phone icon with arrow will disappear from the status bar and your iPhone will start accepting phone calls and forward unanswered calls to Voicemail.
6. Install Updates
Sometimes, the problem is due to an iOS or Carrier update waiting to be installed on your device.
1. Go to Settings > General > About.
2. On the next screen, tap on Install (if Updates are available).
7. Set Date & Time Automatically
The problem could be due to Incorrect Date & Time settings on your iPhone.
1. Go to Settings > General > Date & Time.
2. On the next screen, enable Set Automatically option.
After Enabling Set Automatically option, make sure that your iPhone is showing the right time and Time Zone.
8. Reset Network Settings
Note down the password for your Wi-Fi network and follow the steps below to Reset Network Settings on your device,
1. Go to Settings > General > Transfer or Reset iPhone > select the Reset option.
2. On the pop-up, tap on Reset Network Settings.
3. Enter your Lock Screen Password > On the confirmation pop-up, tap on Reset Network Settings to confirm.
If the problem is still not fixed, call the customer support of your mobile service provider and see if they can help you in fixing the problem.