Got a notification this morning offering an update to my voicemail, to enjoy "premium, ad-supported features". Who wants ads in their voicemail? I called Sprint, and while they can't stop the update from being offered, there's a way to at least stop the notifications. Just go into settings--> more--> application manager--> all (swipe left). Scroll all the way down to voicemail, open the entry and disable "show notifications". It'll still want you to update if/when you use the application, but at least it'll stop nagging you in your notification window about it. Personally I use Google voice for voicemail, so the notifications were my main concern.
Just posting this in case other people see something similar.
Just posting this in case other people see something similar.