Abstract: Trust ratings are embedded in certificates of calling devices in a Voice over Internet Protocol (VoIP) communications system. A method of managing trust ratings involves automatically accumulating complaints concerning VoIP calls initiated from calling devices, and comparing respective quantities of accumulated complaints associated with each calling device. When a quantity of accumulated complaints associated with a given calling device exceeds a given threshold, a trust rating of the given calling device is reduced. In subsequent VoIP calls the given calling device attempts to place, the reduced trust rating is included in the call request so that the subsequent calls are subject to more austere call screening operations than calls having the unreduced trust rating. Call recipients thus affect the calling device's trust rating simply by entering complaints associated with received calls. The method effectively combats spam over Internet telephony (SPIT) through participation of called parties.