Simon Woodside;
Yes, and towards a possibly more contentious application, see Voice over
IP. Lots of VoIP work is being done without involving the internet at
all. Used by telecoms for telecoms applications, where "best effort"
isn't good enough because it needs to keep working when the power goes
out. IP, yes, Internet, no.
Why, do you think, the Internet may stop working when the power
goes out?
It should not, which is required to certain ISPs by regulation at
least in Japan.
Against that you have "voice over internet" which is AKA "voice chat"
and already abounds in true internet p2p apps like iChat, GnomeMeeting,
and some programs on that other OS. These run on the public internet and
benefit from the IETF design paradigms like edge-to-edge (aka end2end)
and best effort but also have to accept the relevant drawbacks.
"voice chat"? Are you assuming PCs?
POTS telephone devices and terminal adaptors is the natural way
of "voice over the Internet".
Note that end to end architecture means ultimate availability of
fate sharing.
Masataka Ohta
PS
According to the end to end principle, end user equipments should
have their own power backup, of course, which is also the case with
ISDN TA or cellular phone devices. Then, with multihoming, your
connection is a lot more robust than that of a single telephone
company.