While LG will most likely not be upgrading the low-end LG Optimus One P500 to Ice Cream Sandwich Android 4.0.4, we already have a port of CyanogenMod 9 for the P500. The development is currently in Beta stage with most of the things working. 
What doesn’t work:
- Wi-Fi tethering
- USB tethering
- Offline charging
- FM Radio: not implemented in CM yet
- Camcorder
HOW TO INSTALL
- Download the ROM from here and GAPPS from here.
- Boot into recovery.
- Wipe data/factory reset, format /system, format /boot, Wipe Dalvik Cache.
- Flash ROM.
- Reboot
- Go to recovery again, flash GAPPS and reboot.
There you have ICS 4.0.4 / CM 9 on your LG P500. 
P.S. – You need to be using new baseband.
