A vertical service code (VSC) is a special code dialed prior to (or instead of) a telephone number that engages some type of special telephone service or feature. Typically preceded with an asterisk, or * (star), key on the touch tone keypad and colloquially referred to as star codes, most are two digits in length; as more services are developed, those that use 2 or 3 as the first digit are sometimes three digits in length. (from Wikipedia)
Verizon Calling Features Activation and Deactivation Codes

Feature Activate Deactivate
*69 * 6 9 * 8 9
Anonymous Call Rejection * 7 7 * 8 7
Busy Redial * 6 6 * 8 6
Call Block* * 6 0
Call Forwarding * 7 2 * 7 3
Call Trace * 57
Call Waiting/Cancel Call Waiting Hookswitch *7 0
Per Line Blocking * 8 2
Per Call Blocking * 6 7 Hang Up
Speed Dialing 8 * 7 4
Speed Dialing 30 * 7 5
Three-Way Calling Hookswitch


* In some areas, press 3 to activate Call Block.

 
Rotary Instructions for Star Codes
Instructions for FiOS Digital Voice Calling Features