The first thing all mean the same thing. Which is using IP

(Internet protocol) for voice services. Some voice networks

are only packet-switched and have no access outside of

their own VoIP network. Most VoIP networks have a Gateway

that connects to a circuit-switched external network which

gives them acces to external calling. One of the gateways

responsibilites is to convert G.711 Circuit-switched media

(typically a T1 provided by a telco company) to the 7.723

Packet-switched media that will traverse the companies VoIP

network. A device called a gatekeeper will then convert the

IP address (used by H.323 protocol) to a standard telephone

number (E.164 address) that can be used for external

calling.

A converged network is a network that passes both Voice and

Data over the same set of devices. Converged networks

generally implement QoS (Quality of service) on all actived

network devices to ensure the VoIP has priority over

standard data because of it's more rigid demands.