Phone numbers (and physical addresses) are examples of semi and fully federated systems. You use the standard and establish contracts and your teleco or post office and connect to anyone else in the world.
Your Google Hangouts/Skype/Facebook are closed, walled garden, proprietary systems.
Keep that in mind.
But from a UX standpoint they are vastly superior to having to deal with people trying to reach me on my US number while I'm in China, or trying to reach one cell phone when I'm carrying another.
Also, the telco operators love to nickel-and-dime consumers for things like roaming charges. I'd love to see more competitors come out and overthrow those rascals by doing everything over IP, creating worldwide MVNOs and slashing all roaming charges to essentially zero. Google Fi has done a nice job. Granted they exist to promote Android, but when I tell friends I have LTE data in 100+ countries without roaming charges, international voice calls for pennies directly from my cell phone, and viewing voice charges in real-time, they are all astounded. Unfortunately yes they too are a walled garden, but the user experience is amazing.
That said, while phone calling has fallen out of favor, phone numbers are still the main form of 'identity' people have, and if anything the dominance of WhatsApp/Messenger has made it more common in my circles to share a phone number rather than a FB username.
- Representing a person by a country-specific number is a horrible UX. All of my contact methods besides phone number remain the same no matter where I am in the world. Several of my contact methods (Facebook, LinkedIn) enable directly "dialing" my real name and intelligently locating me by social proximity instead of asking the customer to program in a stupid number (or multiple numbers) for every contact. A few (Skype, Hangouts) at least allow for alphanumeric, easy-to-remember identifiers instead of numbers. Aren't we in 2017 already?
- I want information to flow with me, not be tied to a particular device. Ideally, I should not have to carry any particular device, but rather present my credentials to any device I own (be that a computer, one of my many phones, tablets, or smartwatches). All of my contact methods besides phone number and WeChat are device-independent and align with this vision.
- E-mail replaces SMS. It supports >140 bytes. In fact, it can comfortably support several MEGAbytes per message! Isn't that mind-blowing? There is ZERO reason to continue to use a stupid old technology with a 140-byte limitation. As part of the deprecation process, I have all SMS go to my e-mail inbox instead of using the SMS interface on the phone.
- I don't take unscheduled voice calls. In general, if my day is going as planned, 95% of the time I am doing something where I shouldn't be picking up a phone (either for my own safety or due to etiquette). That includes machining metal, having dinner with real people, listening to concerts, meditating, coding, hiking (usually without reception), biking, whatever. Unscheduled voice calls are incompatible with my lifestyle.
- When scheduled, I do video calls more often than phone calls.
As such I'm totally fine with a phone app being third-party. A phone number is not the main reason I have an LTE device in my pocket.
In fact, of my multiple LTE-capable devices, only one is capable of receiving phone number calls. The rest have data-only SIMs.