My wife's phone had the same issue. To resolve it I downloaded a copy of the full FC09 update from XDA, made Nandroid backup of rooted EL30, Odined to stock FC09, rooted updated FC09 version, then did Nandroid Advanced restore of data only. Worked perfectly. Recovered all SMS messages, contacts and applications. It's my understanding that as long as you use the same file system, which EL30 and FC09 do, you will have no trouble doing a data restore. Hope this helps.
And by the way, I am new to some of this stuff, so if I am incorrect, please correct me.
Carl
Carl, this worked just as stated. I set aside some time and fixed my phone last night. The first attempt, Odin biffed at "Factory NFS" or something. I made the mistake of yanking the USB cable and then it wouldn't power on at all. I forget exactly what it was I did to get it to wake up after that, but I was sweating bullets for a little while. If that stage of the operation takes more than a few minutes, it's wadded up. You need to try again.
BTW I was using the cleanGB version before i started. I let it "repartition" which apparently you have to know what you're doing so you don't screw things up. I got lucky and didn't know what I was doing, but didn't break anything.
I got the files from "*OFFICIAL* SPH-D700-FC09-8Gb-REL.tar.md5 - xda-developers". I did do the Nandroid backup. (in case you don't know, power off, then power on with vol down, camera, power. Choose backup (I think) and create one.) After loading the stock image, it rebooted and was back to factory (desert rock wallpaper. Sprint crap on the home screen). I then applied the same SU file I already had from before, did the Nandroid advanced restore / data only, and it came up with all my apps and with my wallpaper and most of my settings. However, Juice defender didn't keep my options and I had to re-apply them.
There is a video in that xda developers thread that is pretty straight forward.
So, to summarize, what you are doing is backing up your applications and settings (nandroid), loading the Sprint build that you'd have if you were stock and gotten the over the air update (which unroots you), then re-rooting and restoring that backup. You don't lose anything. You don't have to use titanium backup to restore. you don't have to go to google play and download anything.
Thanks a lot, carl for the straightforward explanation.