Most RIM employees don't get to see the BB Infrastructure. But it's basically a room with lots of oracle servers that act as giant phone directory. All the BlackBerry Servers connect using the SRP and auth key to the BB Infrastructure

(Last time i checked the North America and Asian Relay where in Canada and the UK/EU Relay was in UK just down the road from Heathrow)

Whats to elaborate on thought it's a place with servers and as has been proved in more than one occasion not very much redundancy.

There are many diagrams on how the infrastructure works and how messages get transmitted and what happens. I can elaborate if you want to know how the messages get from one place to another and what the actual process is