Re: visual voicemail
Welcome to Android Central! Which device? Is this Verizon Visual Voicemail?
In general, you can find an app's notification settings by opening that app, tapping the menu button (or swiping in from the left), then Settings, then looking through the app settings for a notification option. The other method is to go to Settings>Apps, select the app, and uncheck the "Show Notifications" checkbox.