A method and system for monitoring calls being made from a cellular phone and preventing calls being made to unauthorized numbers, as defined by the owner of the cellular phone. A security challenge is issued to a cell phone user when a suspicious, previously unknown telephone number is attempted to be called. Approved/safe numbers and/or area codes are stored within the phone and/or in a subscriber's account accessible and updated via the Internet. If the user is unable to provide the correct security code in response to the challenge, the user is prevented from making the call to the particular number.