4. Reset your pin. Maybe you have forgotten your pin or passcode or you never set it up in the first place. This is a common issue. Most carriers have detailed instructions for changing passcodes. For example, to change a T-Mobile passcode, hold down the "1" key, then press the star key, and then press number 5 to go into passcode security. Then press 1, and you will be able to change your passcode. You can change your Sprint passcode online by choosing the my preferences tab and then the "things I can manage online" section. You can reset your pin by calling the carrier if you have forgotten it or never set it up at all. Some sites allow you to do this online.
dialling 123 from your phone and following the instructions.dialling 07782 333 123 from any other phone and following the instructions.dialling +44 7782 333 123 when you’re abroad and following the instructions.

Check your voicemail on iPhone. In the Phone app , Visual Voicemail (available from select carriers) shows a list of your messages. You can choose which ones to play and delete without listening to all of them. A badge on the Voicemail icon indicates the number of unheard messages.
Alternatively, if you simply want to alter your voicemail message to something else, you can do so.