To listen to a voicemail message, fromthe home screen select the Phone app. Note:Alternatively, you can check your voicemail messages byselecting the Phone app from the home screen >Select and hold the 1 key > if prompted, enter yourvoicemail password > follow the prompts tolisten to your messages.
Make sure that you have the latest version of iOS. Check for a carrier-bundle update: Go to Settings > General > About. If an update is available, a message will ask you to update. To check your cellular network connection, try to call someone.

To unblock a previously blocked number when you still have their voicemail message:
The default voicemail greeting on theiPhone plays generic Your call has been forward to anautomated voice message system recording. If your phone is forpersonal use, create a personalized greeting so people hearyour voice and know they called the right number. Open the Phone app . Press and hold "1" to call your voicemail. Enter your PIN and press "#". Press "*" for the menu. Press "4" to change settings. Press "1" to change your greeting. Follow the recorded instructions. On your Android device, open the Voice app . At the top left, tap Menu Settings. In the Voicemail section, tap Voicemail greeting. Tap Record a greeting. Tap Record . Record your greeting, then tap Stop . Choose what you want to do with the recording. To listen to therecording: Tap Play .