Ok, I think I figured out how to change the speed dial for #1.
Go to Settings --> Call, and change the "Voicemail Service"
You can change it to "Your Carrier" or "Google Voice". in order for me to make this work, I had to change it from "Google Voice" to "Your Carrier" for the time being.
Then it'll present an option that says "Voicemail Number" and let you key in any number you want. Your wife's number, your escort service, your actual google voice voicemail number (instead of your cell number, which would bring you to your carrier's voicemail service), etc., etc.
After you're done, return back to the "Voicemail Service" option and revert it to "Google Voice" and you're done.
Now, I still don't think there's a way to change #2, but this fixed #1 for me. One caveat, each time Sprint updates my Evo with a new version of the sprint voicemail application, I have to do this again and again. Pfff...