Do you have it as one of your convenience keys (the "hot keys" on ether side of the device)? If so, go to Options>Screen and Keyboard. You should see "Right Side Convenience Key Opens" and "Left Side Convenience Key Opens" options. You can change these to any app you have on your Berry.
__________________ 1st Step in Troubleshooting: Do you have a BlackBerry Data Plan? 2nd Step in Troubleshooting: Pull the Battery.