AT&T LogoCLASS codes, Vertical Service Codes (VSCs), or the ‘Star Codes’, were all names for a list of codes developed in the late 60’s and early 70’s by AT&T Bell Labs. These codes began with an ‘ * ‘, and allowed PSTN customers to mail their phone companies large amounts of money. In exchange, users were able to enable fancy PBX features on a per-call basis. All of these codes preempted the dialing process, and were usually 2 or 3 digits in length (although each telephone provider may have their ‘own’ unique list).

By the way, the name VSCs harkens back to old legacy telephone stuff. Back in the days of mechanical switching, a ‘vertical’ referred to moving ‘up’ inside the local CO, instead of sending the call out to another telephone provider.

Without further adieu, here is the internationally standardized star treks that your phone can take (err… provided that your telephone provider believes in international standards, and not ‘their own’ standards). Don’t forget! These codes cost some serious paper! AT&T charges up to $7.50 to ‘set up’ the use of a single star code, in addition to recurring monthly fees.
Remember to whisper a little thank-you to AT&T Bell Labs whenever you fire off a star code (or your monthly payment)! Oh, and one more thing… these are for TONE calls only, not PULSE dialing (for all you still carrying rotary cellphones).
 
AT&T Bell * Codes
*02 DeActivate – *66 Notification on Busy Signal
*03 DeActivate – *66 Notification (One Time Only)
*12 Call Assitance (Police)
*30 Cancel Forwarding
*31 Automatic Forwarding
*32 Notify
*40 change forward-to number for customer programmable call forwarding busy-line
*41 six-way conference calling activation
*42 change forward-to number for customer programmable call forwarding don’t answer
*43 drop last member of six-way conference call
*46 french voice activated network control
*47 override feature authorization
*48 override do not disturb
*49 – disable long distance special ring
*51 Intercom Ring I
*52 Intercom Ring II
*53 Intercom Ring III
*54 Extension Hold
*57 Call Trace
*60 Call Screen (Selective Call Rejection)
*61 Selective Distinct Alert
*62 Selective Call Acceptance
*63 Selective Call Forwarding
*65 ICLID Activation
*66 Busy Call Return
*67 Call Display Block
*68 Computer Access restriction
*69 Last Call Return
*70 Call Waiting Disable (Per Call)
*71 Three-way calling (Per Call)
*72 Activate Call Forwarding
*73 DeActivate Call Forwarding
*74 Speed Dialling (8 numbers)
*75 Speed Dialling (30 numbers)
*77 Anonymous Call Rejection
*80 Call Screen Disable
*81 Selective Distinct Disable
*82 Selective Acceptance Disable
*83 Selective Forwarding Disable
*85 ICLID Disable
*86 DeActivate Busy Call Return
*87 Cancel Anonymous Call Rejection
*89 DeActivate Last Call Return
*90 Re-Activate Call Forwarding Busy
*91 De-Activate Call Forwarding Busy
*92 Re-Activate Forwarding No Answer
*93 Call Forwarding No Answer (*91,*93 to completely disable)
*94 Ring Control (Call Answer)*95 Message Monitor (Call Answer (link|flash) to interuppt/talk))
*97 check if you have messages, remotely (on=2beeps,off=4beeps)
*98 Call Answer