It's not the plumbing, it's the infrastructure. Running the public telephone network costs more than running Internet infrastructure. There's a lot of old, crufty regulation that still applies to POTS (plain old telephone service delivered on copper), so unless your phone company offers flat-rate domestic calling, you're going to have to pay extra for long distance. Telcos aren't particularly interested in doing things to promote the use of POTS because it's not as profitable as it once was.
If people don't mind getting used to the idea that they won't have a phone number anymore, voice over IP (VoIP) is fully capable of getting calls anywhere in the world with no additional complication or cost. It does mean giving up your phone number for a SIP handle like
blrfl@blrfl.org and getting a VoIP phone set up.
My home phone's been on VoIP for years. I pay $8.00 a month for my provider to maintain a phone number and terminate my incoming POTS calls. Since I rarely use it for outgoing calls, I'm on pay-as-you-go, which is $0.02 per minute. Flat-rate, it would be $20.