Nokia 6030
lock keys
To lock: 1) Press center button, then
2) Press *.
To unlock: The same sequence again.
In lock mode, you can receive but not send.
The 6030 is, frankly, a tad on the flimsy side, so you sometimes have to enter these codes more than once before they 'take.' Once locked or unlocked, the screen confirms it.
Good luck!
marindavid