The fundamental change to telephony service that VoIP portended affected a number of constituencies. Start-up companies, as well as large, established phone companies and cable television providers, offered VoIP calling plans that could substitute many of the phone services sold by the same or other established providers. These same providers might also benefit from VoIP by using it to enter new markets. Other companies that previously had nothing to do with telephony could become VoIP telephone service providers: For example, the necessary software codes to make VoIP calls had been written into Microsoft's XP operating system through its Instant Messaging feature. However, IP communications represented a fundamental challenge to the complex web of federal and state regulations that governed telephony. Because VoIP telephony was not tied to physical telephony networks in specific geographic regions, it raised the question of whether federal or state regulators would have jurisdiction over VoIP services and how jurisdiction would be exercised.
