A method, a system and a computer readable medium for routing packets across disparate networks are disclosed. For example, the method receives, via a media gateway controller (MGC), an external request from an external requestor for a reservation of a public switched telephone network (PSTN) trunk on a media gateway (MGW) for a communication session between a voice over Internet protocol (VoIP) network and a PSTN network, sends, via the MGC, a H.248 request to the MGW to make the reservation, establishes via the MGW, a communication path and sending a message to the MGC, retrieves, via the MGC, an assigned Internet protocol (IP) address and IP port on the MGW from the message from the MGW, sends, via the MGC, an allocation request to a media terminating session border controller (SBC) and allocates, via the media terminating SBC, a public IP address and a public IP port from an available pool of IP addresses and IP ports at the media terminating SBC.