There are tons of forum posts, guides, comments, wikis regarding android rooting, goldcards, overclocking etc.
It’s quite confusing.

I’ve personally tried several procedures to unbrand the phone, this is the one that worked as expected.
It’s simple and effective and you just have to exec steps from 1 to 7:

http://www.androidiani.com/forum/modding-lg-optimus-one/57132-guida-aggiornamento-gingerbread-v20c-v20g-recovery-21-11-2011-a.html

I’ve succesfully unbranded an LG Optimus One P500 phone, upgrading to Android 2.3.3.