[EDIT: These are the standard codes used by most land line carriers. Cell phone or VoIP providers may not use all of these codes, or have different codes]
*77 Activate ACR (block private callers) FREE w/CID service
*87 DEactivate ACR FREE w/CID service
*82 UNblock restricted number to show your CID per call FREE
*67 BLOCK CID info per call FREE
*72 or 72# Activate call forward SUBSCRIPTION SERVICE check carrier for rates
*73 or 73# DEactivate call forward SUBSCRIPTION SERVICE check carrier for rates
*57 Call Trace POSSIBLE PER USE FEE check carrier for possible charges, or 1-866-trace-4-u for more into on this feature...
*69 Call back (provides number of last call) PER USE or SUBSCRIPTION SERVICE check carrier for rates
*70 disable call waiting per call (use this before number for dial up networking so you do not get kicked off line by call waiting)
all star codes can be accessed with a rotary phone by replacing the * with 11 for example *69 would be dialed as 1169 on a rotary phone....