[drdaeman]

For me, an year ago, TextSecure's primary selling point was that it wasn't reinventing the wheel, but was layering above the already existing network. Something very resembling how one installs an OTR plugin for their XMPP client, except for being an app (since, unfortunately, I have yet to see an mobile messaging app with a sane plugin system).

I've perceived their own proprietary data transport as progressive enhancement that enables to cut the costs, not as a primary option. I.e. SMS transport being the core option, not a fallback. Personally, haven't bothered to use data transport at all - it was unable to handle multiple identities anyway.

Sadly, I was mistaken.

[tasn]

Their protocol and implementations are fully open source. https://github.com/WhisperSystems

[drdaeman]

So?

I use the term "proprietary" in sense that it's their own unique protocol that nobody else uses. (Don't tell me about their interop with CM, its partnership, not federation.) Or you know some alternative compatible SMS apps that use libaxolotl or Axolotl protocol? I don't. Would love to hear there are some.

[tasn]

Fair enough, they do "own" it, and can change it at their own discretion, and that is always bad. However, that's how many standards come to life. See SPDY and HTTP/2.0 and probably (no facts to back this one) most of the XMPP XEPs.

Not sure about the SMS side of things (which is being dropped anyway) and how things work there, but using the phone number as an identifier makes federation without a central authority infeasible. I've been wishing since day one that they'd allow xmpp style usernames too in order to make federation possible.