None of the local exchange carriers have any plans to replace their 5ESS or DMS TDM switches.
Lucent is not producing a replacement for the 5ESS. Nortel is effectively no more.
That effectively puts the last few nails in the coffins of POTS.
All new systems are mostly Broadsoft switches. Full IP with TDM gateways.
Most of you probably have POTS lines coming off your local 5ESS, DMS or maybe even a few AXE's.
Eventually those will be replaced. There will be some far off Broadsoft controller, likely no longer in your local CO, may not even be in the same state. There will be a local gateway for those that hang onto their POTS lines.
With few exceptions, all of the old "toll circuits", interoffice connections are all IP. Probably few SONET rings out there still, but IP is a whole lot easier. SS7 networks make it a no brainer. Why run circuit switched systems when IP is so much easier, flexible and cheaper.
Local to me, AT&T has already announced the end of conditioned circuits for radio systems. I've got to have a replacement working by 2020, or so I'm told. It'll have to be IP of some sort.
Sure POTS will hang on for a while. It makes sense, it's cheap, it works. Problem is the stuff that makes it work so well is failing. Used to be AT&T and the larger carriers had huge teams of outside plant cable techs and engineers. The large scale copper cable plants were the backbone of this country. As those guys retired, or were pushed out, the copper plant has suffered. The knowledge and experience to keep those systems going disappeared. To be fair, they were costly, the infrastructure was no longer cost effective, and some times they were just a plain old eyesore. It'll be kept marginally running as long as it makes sense.
Back 30 years ago fiber optic cable wasn't cost effective for use from the CO out towards the customer. That's changed. Cable is cheap, always has been. The end devices were expensive, but not any longer. Technicians have been trained on how to work with fiber, fusion splice, test, etc. It's no longer the specialty it once was. I remember the term "fiber prima donna" being a poplar "insult". We had guys that would only touch fiber, and would never lower themselves to the position of working on copper. Used to annoy the hell out of us, but as times changed, training caught up. Now, it's sort of the opposite. Finding a tech that knows how to properly test a copper pair is hard. Finding one that knows how to use a sidekick meter properly and can accurately locate and identify faults is rare.
There's a lot of reasons analog POTS is going away. There isn't any one reason that's better than the other. In the end its all about costs. Dedicated copper pairs from a TDM switch all the way out to the customers phone doesn't make financial sense. Multiplexing telephone service onto a IP fiber circuit is much cheaper. Where things will continue to change is on the "last mile" part of the circuit. It's easy to take fiber to the local cross connect box, install a terminal and then hop on the existing copper pairs into the customers homes. Not only does this provide a cost effective solution for telephone service, but piggybacking on data services is simple. What we are already seeing is the local carrier finally replacing the "last mile" copper with fiber. One of my coworkers just had AT&T pull fiber right up to the terminal on the side of his house. Probably within a few months his copper pair will be abandoned.
A few years ago I did a cost analysis of taking my PBX from PRI trunking to IP based trunking. At that time I was running 10 PRI circuits to/from the local exchange carrier and a couple to a long distance carrier. I still had about 100 analog trunks as backup.
I priced out a redundant set of -48 volt powered session border controllers to sit on our network border and handle the interface/security with the carriers. Figuring on having to replace those every 5 years or so (pretty normal lifespan for anything IP related), plus the cost of the trunking, it was considerably more than the PRI served trunking I had at the time.
I'm getting ready to do that study again. I already know the SBC's have dropped considerably in price. The carriers have started lowering their costs for SIP trunks.
Within a year I'll probably be running 90% of my traffic over IP.
If you go to Eastern Europe, you'll find that wired telephones are becoming a rarity. Just doesn't make sense to build out a big cable plant to sparsely populated area with low income. I was in Romania many years ago and there was no copper cable plant in most areas. What there was, new cellular towers. Everyone had a mobile phone.