Busy line

The busy line is the state where a caller hears the busy tone: you're already on the phone, call waiting isn't enabled or is saturated, and the network has nothing else to offer. Technically, it's a clean rejection; commercially, it's a closed door without even a mailbox — the caller can neither leave a message nor wait.

It's the most avoidable missed-call case: the cause is neither absence nor rest, but success itself — they call you because you're good, and you lose the call because you're on the phone. The fix is a setting, not an effort: conditional call forwarding "on busy" to a system that takes over — instant text, voice agent, or voicemail as a last resort.