Waaaay back at CES in January, Sprint and RIM announced that they were cooking up a version of the BlackBerry Playbook that played friendly with Sprint’s 4G network. And then… nothing. Months went by, with nary a mention from either of the companies involved.Alas, it looks like the Sprint 4G Playbook will be buried before it’s even born. Blaming a “lack of demand from business customers” (read: everybody who wants a tablet right now probably already has an iPad or a Xoom), Sprint has killed off plans to launch the device.