I misspoke, I should have said SIP over fiber or cellular. I also just focused on voice and not data. We were told 5 years ago by our carrier to get off of copper. The copper infrastructure is no longer being maintained, have a nice day. It used to take 24 hours for a service ticket for copper repair, now it can take over a week.
The local carrier has been spending money putting in fiber 'everywhere'. Much more bandwidth, better lightning protection, etc...
Internally we emulate analog lines with voice gateways; we still have users that 'must' use fax machines; think lawyers and HR, the credit card machines have all been moved over to cellular service as we won't even deal with PCI compliance on our network.
The carrier does the same for those sites that still need 'copper lines', bring it in on fiber and then emulate POTS.
I get that the transition is uneven and there are a lot of factors to contend with but it's happening simply because it is cheaper in the long run for the carrier to pull away from copper. I know the carriers were given boatloads of money to provide service to rural areas, but honestly, does anyone think they actually give a flying fuck? That's just more money in their pocket increasing share holder value. There is no screwing like getting screwed by the telephone company, lol.
Eventually I see fiber for the backbone( already there but growing) and cellular(towers are going up everywhere) for the last mile and even then only in certain situations where it is profitable to do so. If the carrier can make money then they will provide the service.
I currently have fiber to the curb and it's brought into the house on coax so I am already there. I gave up the land line 10 years ago along with the answering machine. But that is not the case for everyone...
Sorry for being all over the place, I am 40 ounces of coffee into it and it's all just stream of thought :)