You can't format the phone memory though you can re install the firmware . The code *#7370# restores the only factory settings. Upgrade using this link:
The reason for formating the phone is it has become sooooooo lazy.It boots up for decades and if you go to the music player you can go and come back from picnic to see the songs list. All this in a half filled 1gb card.
Ya... I'm going to upgrade the firmware on your advice. I'll post the result if i see any improvement.