Would just like to add I was able to flash a LG Optimus S to PP for talk/text for my mom. Haven't tired to get MMS or Data working as my mom doesn't really need it.
Thought I would add it to make it easier for people.
You need to install the USB drivers. After that plug the phone in once without debugging on and for all the drivers to setup.
Once that's done unplug enable USB Debugging and then com ports will show up and your good to re-flash it with your software of choice.
Make sure to re-write or find your SPC/MSL code first.
NOTE: You must be running a stock or stock based ROM to flash the phone. Custom based roms WILL not be able to flash the phone. If you plan to install a custom rom make sure to flash the phone first or else you will have to revert back to stock.
yeah I've done this phone in the past also. My experience dictates do not go this route but buy a used Verizon phone and sell off the Sprint based phone as it's takes a some time fiddling getting getting it up and running.