Which mobile messenger is currently considered secure? I know of two messenger apps: Threema, which is not open source and telegram, which has its own crypographic routines, which have been cracked at least once (as far as I understand it). Is there any recommendation (please include a link/source).
TextSecure from them has a lot of good people behind it (Moxie Marlinspike being one notable). It is open source, actively developed, and they have plans for an iOS and desktop client on top of the already existing Android client. They support both SMS and data for sending messages. It is aesthetically pleasing, simple to use, and supports group chat. I highly recommend it. Their blog has some interesting posts about some of the crypto its built on, if you're also interested in that stuff.
[1] https://whispersystems.org/