Re: VOIP doesn't need much bandwidth
"VOIP doesn't need much bandwidth at all, a few tens of kilobits/second if that."
Depends where you look/measure (and has done for years, and will continue to do so).
At the end user end of the setup, e.g. most homes, offices, etc, the IP protocol overhead massively exceeds the bandwidth of the conversation itself, if there's only one or two phone calls on the wires. But you try getting more than one or two VoIP calls over a couple of Mbit of bandwidth and you're heading for trouble, bigtime.
And don't forget that for intelligible voice conversations, latency can be quite important too. Latency often doesn't improve as bandwidth increases; often quite the reverse.
"I think probably 99% of cordless phone base stations have no battery."
Maybe so, but that's currently fixable with a couple of boatloads of line-powered phones. Lose line power, and more importantly switch the backbone to cheap IP kit (they're not moving to IP to improve service, are they?), and then how do you fix the "wide area power loss" problem.
Ask someone who was in Lancaster when it mattered.