Until quite recently (i.e. with the introduction of NGNs), it's my understanding that in the US, calls to mobile phones were (and probably often are) still rout

Until quite recently (i.e. with the introduction of NGNs), it's my understanding that in the US, calls to mobile phones were (and probably often are) still routed to the geographic location of the phone number's rate center. People don't usually think about it because intra-US latency is usually low enough to care (and lower than the latency to most outsourced call centers in any case), but during natural disasters such as Katrina, the ties between geography and network topology still make themselves known.