Tap on the Voicemail tab and select the voicemail you wish to manage

 

From here, you can play the voicemail message, call the number back, delete the voicemail message, or mark the voicemail message as read

 

In the voicemail tab, tap on the plus icon and tap Call Voicemail

 

To enter your passcode, tap the Dialpad icon from the active call view

 

And enter your Voicemail box passcode followed by #