I have to commend Sprint on this one. While most carriers are afraid of Google Voice (or any change) Sprint seems to embrace it. They just announced that they will be launching an integrated Google Voice experience on their network. They will allow customers to set their existing Sprint wireless number as their Google Voice number. You will then be able to use Google voice without having to port your number which will be available to all Sprint CDMA phones.
This means you will be able to use Google Voice for call routing, screening, blocking, recording, voicemail, and more. You can sign up to be notified when this feature is rolled out at this link though more details can be found in the press release.