A telephone call-routing system comprises a routing intelligence adapted to receive real-time activity reports on busy status of remote telephone stations, and to route incoming calls based on the busy status. In a preferred embodiment the routing intelligence sets a busy semaphore for each station to which a call is routed at the time the call is routed, before a real-time signal is returned that the station is in fact busy. The semaphore is initially set to busy for a first period of time substantially equal to the known latency for returning the real-time busy signal. After the first period of time, and with return of a real-time busy signal, the semaphore is reset to busy for a second period of time substantially equal to the historical average elapsed time for calls in the call-routing system, after which the semaphore is released. After the first period of time, and in the absence of the real-time busy signal, the semaphore is immediately released so further calls may be routed to the station.