Find "Mobile Network"
Press the Menu key twice.
Scroll to Options and press the Navigation key.
Scroll to Networks and Connections and press the Navigation key.
Scroll to Mobile Network and press the Navigation key.
Turn data roaming on or off
Scroll to While Roaming and press the Navigation key.
Highlight On or Off and press the Navigation key.
Exit
Press Disconnect.
Press the Return key to return to standby mode.