Originally Posted by Yeagermeister
Can you use a custom rom if your carrier hasn't upgraded to 4.0?
When you unlock and root your phone it allows you the ability to run a custom ROM.
Nothing really changes.
If you go the ROM route I suggest following this guide:
Pretty much teaches you everything you need to do.
If you feel like being a nerd and want to do it the hard way i.e. using command line then it can be a little more involved.
But, fast and easy method:
1) Use WugFresh's tool to unlock and root.
2) Use a launcher like Nova etc so that you can backup your homescreen settings etc.
3) You can use Titanium backup to save app data i.e. saved games etc.
Always make a complete backup before you flash a new ROM!