There are three methods available. The first and second one are recommended. If you are uncomfortable with adb and command prompt please use method one
UPDATE: This has been confirmed as working on T989!
Method 3 is only to be used if one and two fail, or if you are positive your efs is corrupt!
Original source for solution, with a few method changes by me:
1.) Use busy box installer from the market and re-install even if u have it working
2.) If step one doesn't work, install super su updater, and update it, then try step one again.
3.) Boot into cwm and dark side wipe 3x
4.) Flash rooted 2.3.5 from thread below
5.) Boot into rom and install root explorer
6). Navigate to /efs/imei/
7.) Press menu and select new file
8.) Name it "keystr" exactly as in quotes
9.) Long press keystr and select edit in text editor
10.) Type "ON" and press back, selecting save.
11.) Reboot and make sure keystr file is still present.
12.) Now u have a few options. U can flash ics back using either Odin one click (UCLA4 or UCLD2), but I don't recommend this. Flash one of the ics roms from the development section, we have great devs!
Rooted 2.3.5 zip:
1.) You must have the Samsung drivers installed for the skyrocket, available from here:
2.) Once installed, download the attached zip, its a copy of ADB with the needed file inside
3.) Unzip to any location
4.) Boot phone into cwm
5.) Go into Mounts and Storage, and select "mount /efs". Once done connect usb cable to phone and computer
6.) Open command prompt and navigate to the unzipped adb. Issue the following command "adb devices" it should list phone
7.) Now issue the following command "adb push keystr /efs/imei"
8.) Reboot phone and check presence of keystr file in /efs/imei directory with Root Explorer
Flash attached EFSFix.zip in cwm and reboot.
A SPECIAL THANKS AND SHOUT OUT TO:
mahausrath and Colombiano80 for providing the efs dumps i needed
cmbrown for being a faithful tester!