It's great that there is such a strong interest in secure communication, but all of the solutions that keep getting placed in the limelight in recent years are either centralised or exclusively available for use with a smartphone (because of the phone number requirement), often both!
I'm sure that these solutions are a lot more secure than completely unprotected alternatives, but am I wrong in assuming that if you want secure and private communications, the following principles must be met at the least?
* The protocol used must be open, standardized and implementable by others
* Widely endorsed by cryptography experts
* An implementation must be available and developed as free and open source software
* End-to-end encryption is used for the contents of the conversations, private keys do not leave the user's computing device
* The protocol must not have any technological barriers that prevent an implementation from working on any modern operating system (i.e., a phone number is not required)
* The protocol must allow for a complete communications network (clients and servers) to be implemented without the need for centralised third-party services
(The last point probably implies federation.)
For e-mail, OpenPGP meets these requirements. For chat, XMPP has Off-The-Record messaging.
Some of the above points are hostile towards any party that creates secure communications tools with the intent of growing a large user base for economic purposes. Call me a sceptic, but this is probably why use of these protocols and principals is limited to security experts and software developers who understand these principles — for anyone betting on creating the next WhatsApp in one of the mobile walled gardens embracing the whole list means risking losing your potential advertising eyeballs to alternatives.
Of course, there is also the matter of infrastructure. A lot of people expect to be able to use these tools for free, but that implies that someone is paying for the hosting of (relay) servers.