For phones the demand is very different: a subscribers connection is either in use or not. When it is in use, it typically consumes no more than 64kbps at most. And it is easy to model expected peak demands in normal (non-disaster) scenarios because everyone that people might be calling tends to have a fairly low number of inbound connections, so the total peak bandwidth usage is still quite small - miniscule by todays standards.

When you're paid per subscription, and you at most carry 64kbps through a small local area before long distance fees kick in, it works.

Even so, in Europe (and I believe most of the world) landline usage is metered. It is the US model of free local calls that is unusual.

Landline phones certainly used to be metered for all but local calls.

Devil's Advocate: most dialup internet services are not metered as well.