It is not possible to make the voicemail alert work, at least not that I have found. Since sprint uses a totally different system with the visual voicemail crap.
I think that there is a way to edit the filesystem in bitpim and remove the sprint icons and programs associated with them, it is just that I am not brave enough to do it as i do not want to screw my working phone up.
Try google for adding apps and ringtones to the instinct and you should be able to find the same instructions that i did, i think they were on a sprint instinct forum somewhere, after learning how to do that you will have an understanding of how to edit the filesystem to remove the icons and their associated programs.