I can't check my voicemail on my Apple iPhone 12 iOS 15.0
Cause 1 of 4: Your voicemail hasn't been set up
To check your voicemail, you need to select voicemail settings.
Solution: Call 121 and follow the instructions to set up your voicemail. If you've previously deactivated your voicemail and want to reactivate it, call 1211.
