Joshua Lund at MissingM has posted a comprehensive review of the current options for secure mobile messaging. He’s not afraid to drop the hammer on the less than worthy:
If they can’t be bothered to release any source code, fail to provide even basic protocol documentation, and have not posted a threat model analysis, then they are not worthy of your time or your attention.
He concludes with recommendations for Android and iOS, and the promise of nirvana:
Encrypted phone calls and text messaging bundled together in a unified interface that will be available on both iOS and Android? Hell yes.