A gateway acts as a conversion from one protocol to another or in the case of VoIP from the VoIP network to the POTS network. A router works by looking at the IP address in the packet and decides if it is for internal use or if the packet should move outside the network (to the WAN). In a VoIP conversation, you would have a gateway that works for any calls that can not be carried via IP and it moves them to a POTS connection. You generally need both.
Learn more about IP telephony gateways and their important role with unified communications in our IP telephony gateway primer.
This was first published in April 2005