How do I access my voicemail?

摘要

Q I have an Android smartphone that sometimes shows 'New voicemail. Voicemail number unknown'. Tapping this shows a settings screen, again with a message telling me that the voicemail number is not set. If I tap here I'm asked for a voicemail number. I have to tap Cancel, as I have no idea what else to do. How do I hear my voicemail message? Also, to clear the notification I have to force the app to stop. Is there an easier way to do this?