Methods are disclosed for providing prepaid telephony service via an Internet protocol (IP) network system (300, 500). A first method provides controlling at least one media agent (304) or call routing station/switch (310, 312) of an IP network system (300) for allowing and/or blocking call media streams from traversing through the media agent. A second method provides directing all signaling messages transmitted by a signaling agent (502) or station (510, 512) and all media packets transmitting voice and data communications through at least one common device within the IP network system (500). The methods further provide for continuously monitoring a subscriber's account balance and terminating the prepaid telephony service if the account balance is less than a predetermined amount.