A dialing plan is a set of rules that determines how phone numbers are formatted and processed within a telecommunications system. It specifies how calls are routed based on the number dialed, including local, long-distance, and international calls. Dialing plans help ensure that calls are connected correctly and efficiently, reducing errors and improving communication. In modern systems, dialing plans can be complex, accommodating various features like call forwarding, voicemail, and conference calling. They are essential for both traditional landline services and Voice over Internet Protocol (VoIP) systems, allowing users to connect seamlessly across different networks and devices.