If you want to play online we recommend you buy an e3 flasher. This can downgrade your console but also have a dual boot feature. This way you can have cfw one the console and ofw on the e3 flasher's chip.
Note that to use the e3 flasher on a phat PS3 you will need to do some soldering, with slims I think you can buy a NOR clip which means you do not have to solder. I am not sure about the installation process, I dont have one, but you may be able to look it up on youtube.