I just got the issue of the annoying text (SMS) message with every voicemail fixed. Call the Sprint (or your carrier) support number, and tell them to "deactivate the code for sending an SMS Voicemail Activation". The rep told me there was no code number or name, but it is a feature associated with the BB account.
It literally took the young lady about 1.5 minutes to turn it off from the time she answered. I'm impressed!