Registration Based VoIP providers – require the PBX to register with the provider using an authentication ID and password. Most of the VoIP providers pre-defined in 3CX Phone System are registration based.

IP Based / SIP Trunk VoIP providers – IP Based VoIP Providers (also known as SIP Trunks) do not require the PBX to register with the provider. The IP address of the PBX needs to be configured with the provider, so that it knows where calls to your number should be routed.