Just keep in mind that a Cell South or any non-Sprint branded RUU probaboly won't be useful since the asroot2 exploit was patched in those versions.
I consider us lucky that it wasn't patched in the MR1 RUU release that flip posted.
I would like someone else to try before we call it good. Just some of my notes:
(1) Create & Test a Gold Card (a 2GB SanDisk worked for me). Outlined by markachee in Post #27. You should see something similar to the image attached on post #42.
(2) While the Gold Card is in your phone, run the new RUU:
http://geekfor.me/news/sprint_ruu_156/
(3) After phone reboots, quickly (before first data connection) put phone in Airplane mode (Push down the end call button until the power off options appear, choose airplane mode).
(4) Go to dialer and do a ##3282# (##DATA#) and go to advanced. change the Sprint DSA to something random (i.e.
http://google.com). Press menu and commit modifications.
(5) Turn off airplane mode.
(6) Verify radio (phone calls) and data connectivity. If you weren't quick enough on step 4 you may need QPST to put your settings back in. QPST version 2.7 build 313 worked great for me. Settings for your carrier can be found by googling.
(7) Root your phone as outlined in this post on XDA:
http://xdaforums.com/showthread.php?t=583291