It's got a few years yet, but POTS and mobile are already legacy, they just don't know it yet.
Better hope Apple shareholders don't find out!
It's not the _devices_, per se. It's the network. The infrastructure. And the ability for Google to rely on a phone number per person. It's an invalid model.
And voice comms are occasionally useful, though I make them rarely -- it could easily be months.
The idea of carrying a bundle of angry that can start sounding at any time, anywhere, is a turn-off. Especially if I've no control of who's at the other end.
Two of the primary reasons people carry phones are because others demand that they be reachable, and secondarily, so that the phone holder can reach others. The second I don't mind as much though it's also a crutch.
A device with good text capabilities, that can also optionally receive voice inputs and convert that to text, allows a very* limited whitelist set of calls, and otherwis directs all incoming traffic to a wait or prove your worth queue, would start to approach reason.
I remember the days of five-line dial phones and office receptionists, pre voicemail. It sucked for the receptionist, but coming back or into the office and being handed a stack of message slips was vastly preferable to bouncing through voicemail and having to do the transcriptions yourself.
You won't see that because that is not what makes the phone number so useful. Its biggest benefit is being able to correlate all those separate data profiles via one unique key. This makes these profiles more valuable to advertisers. You won't see advertisements in most of these apps (it would drive users to the competition) but they don't have to; they just show them in the browser. They already know it is you thanks to the ubiquitous social media buttons and tracking going on.
This is largely conjecture, sure, but the fact that using your phone number is a requirement rather than an option makes me suspicious.
Sometimes I don't mind if two services know that I am the same person, but I would like to be able to choose for myself. Sometimes I do like to use a throw-away email address and a VPN to use some service, simply because I care about my privacy. Often I don't feel that a service needs to know who I am beyond an alias.
Chat networks are all moving to the use of phone numbers because users mobile phonebooks are a vendor neutral, open access social network of high value contacts that almost everyone has and for which there are simple APIs available.
Phone numbers have other advantages. They are difficult to register in bulk (it can be done but it costs a lot more than bulk registering web accounts protected only by a CAPTCHA). Regulations in many part of the world enforce the ability to do number porting which makes mobile numbers truly user owned - unlike email or jabber ids which are ultimately owned by the organisation after the @ symbol. There is a simple remote attestation protocol: you can prove you own the identifier by simply providing a challenge code. Everyone understands them. And it outsources identity management costs to the telcos who have large branch/shop networks to help people who e.g. lose their device/SIM. Building out and staffing account recovery infrastructures is a significant driver of costs for large web platforms. For instance if you have a contract then you can recover your identity by physically walking into a local telco shop with your passport, you will walk out with a replacement SIM (and the prior SIM remotely deactivated) a few minuets later. It's partly by shifting these costs to the telco networks that WhatsApp was able to scale to hundreds of millions of users with only 50 employees.
When I look at how things work done this way vs a traditional internet federated network like email, Jabber, IRC etc, I have to agree with Moxie - it's not so bad, actually. I'm not normally a big supporter of government regulations, but making number porting obligatory is a relatively low cost rule that makes the use of phone numbers as the universal id a lot more palatable, because it's truly user owned at that point. Switching mobile networks and switching chat networks is a lot easier than switching email/xmpp providers because forwarding has always been an afterthought in such protocols, is legally optional, and at any rate is always going to be more complicated than just re-assigning ownership of a truly provider independent code.