1. Does the US have number portability anywhere? If so, that would be a /huge/ region, and very interesting to examine to see how they manage it.
In the USA this is called LNP (Local Number Portability). This article has a couple of pages of history and then a technical overview of how LNP works. http://scholar.lib.vt.edu/ejournals/JOTS/Winter-Spring-2001/pdf/obermier.pdf This document explains the architecture of LNP in today's phone network: http://www.verisign.com/stellent/groups/public/documents/white_paper/001950.... However, LNP is not as simple as most laypeople think. It has other applications than simply consumer convenience. For instance, disaster recovery http://www.neustar.com/pressroom/datasheets/DisasterRecPress.pdf Read this description of number pooling http://www.verisign.com/stellent/groups/public/documents/white_paper/001949.... and reflect on how similar this seems to injecting longer prefixes into BGP (hole punching) to support moving a customer from another network. LNP and routing are the same problem. The details of the solutions differ because the technology environment and constraints differ. But you will never understand IP routing unless you understand how non-IP networks solve these same problems. That's why some people use RIP to teach routing even though it is considered bad practice to run RIP on any network in this day and age. People need to learn routing theory separately from "How to configure BGP on your brand-X boxes". --Michael Dillon