neophite question on VoIP bearer traffic

VoIP bearer traffic - the RTSP stream after SIP-setup.
Is this correct:

1) No matter where your SIP server is, the source of the bearer stream can be/is often most anywhere, and likely not in proximity of the SIP server.

2) The bearer traffic source/routing varies according to how the VoIP operator manages outside services, or the VoIP operator may outsource everything and has no influence.

3) Some big VoIP operators have their own private national network (frame relay or ?) and have total control and QoS for the bearer traffic can be better. Some examples might be the cable companies' digital phone and some large corporations' private IP networks.

Noob questions