Rooting & Flashing Custom ROMs is one of the adventures you can embark on an Android phone. There is a very active community on XDA-Developers and other forums porting new versions of Android onto not so new phones. Its fun to resurrect your old phone and give it a new life. Caution is advised nevertheless.

Flashing ICS / JellyBean with Google Now seems to be the in thing now. Yesterday I installed ICS 4.0.4 with GN on my old Samsung Galaxy 4G and boy there is nothing like seeing my old phone dancing to new tunes.