there is a ' master clear' option in the menu- look through the menu under
phone settings, ( maybe security?) etc. you will find it- it will clear all
phone data- calls, phonebook, etc. you will need to enter a sec. passcode-
normally 000000 or 123456 or 654321.

also, to clear your own phone #,

74663 # 1 fcn fcn

when it says enter MIN, enter 1000000000
( or any dummy 10 dig. #)
then STO, then hit STO to get out of programming.