Sprint isn't going to upgrade to EVDO Rev. B anymore, unfortunately. This is their response on Sprint's forums:
"
Sprint is committed to delivering the highest quality network experience. Our Network Vision plan will improve your network experience, but it does not include any EVDO Rev B launch. Sprint has evaluated EVDO Rev B and chosen to go directly to 4G connections. Since we are not launching EVDO Rev B, none of our handsets supports EVDO Rev B.
Thank you for your interest in our Network and Chipset Technologies!
"