I found the guide to a little obnoxious myself, I think we need a post for EACH baseband.
To REVERT to ZVD
1. Go to Settings->About Phone, verify that your phone is indeed an LG LS670 (Optimus S) Not V
2. Back up data you don't want to lose. (i.e. move it to the SD Card) Use Astro, ES File manager, etc.
3.Download Phone USB Driver for phone from
Here.
4. Plug your phone into the computer.
5. Pull down the status bar, and click the USB connected status. When the screen comes up it should be GREEN, press the button to turn on USB Storage Mode.
6. Download the Sprint Official ZVD Update.zip at the link. Copy to the root of your SD Card (As in, don't put it in a folder). Do NOT UNZIP, or RENAME the file.
Sprint ZVD Update
7. Hold Down The Power Button and turn the phone completely off.
8. Hold down the Home, Volume Down, and then The Power key all at the same time. Keep holding until the initial LG logo appears, and then the phone will enter recovery mode.
Note: DO NOT attempt this step if you do not have the LG Stock recovery
9. Select install Update.zip from sdcard. Wait for it to finish. Do it again, then clear the cache, and restore factory settings.
10. Reboot the phone.
11. Do not install any OTA updates if the phone prompts you
12. Go to Settings->About. Verify ZVD Baseband, and that you have a signal. If not repeat steps 9 and 10.
13.Connect your phone to the computer again
14. On the phone go to Menu->Settings->Applications->Development->USB debugging, and turn the USB Debugging ON.
15. Check that phone has USB storage DISABLED, (i.e. Green, not Orange)
16. Temporarily Disable your antivirus, (most give you the option for 1 hour, or until reboot) YES you have to do this step, if it makes you nervous then turn back now.
17. Download this file to your desktop, yes it has a virus, that's how the root works.
OptiAutoSFX.exe
18. Run the file, and choose option A, and follow the on screen instructions. The program says that it might take more than one try, but it has worked on the first try for me every time on ZVD.
19. when completed the program will reboot your phone, and when it reloads you should have root. Check this by looking for superuser as an installed application, and run it. It will report whether it is successful. If not repeat steps 14 -18.
20. This will have a rooted stock ROM. I recommend Quattrimus CM9, or HydroROM for stability. They have their own instructions for install.