A hard reset will erase all data and reset the device to its original factory settings. Use this as a last resort or before selling/giving away your device.
General Technical Reference Date: [Current Date] Subject: Comprehensive reset methodologies for BlackBerry Curve (OS 5.0 – 7.1) reset blackberry curve
If the keyboard shortcut doesn't work (or if you have a model that doesn't support it), the battery pull is the time-tested BlackBerry solution. A hard reset will erase all data and