CLASS 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 […]