I recently upgraded from a Nokia 9300 to a Nokia 9300i - so after I transferred all my data I wanted to give my phone to my wife. Obviously not wanting her to see all my naughty appointments, I needed to format it. It was not intuitive... But finally I figured it out:

• Take out battery for 10 seconds
• Reinsert and open device
• At blue NOKIA text, press and hold Ctrl+Chr+Shift+F until the Format dialog is displayed
• Select Format.

Your device will now be reset to factory conditions.