Whattsapp the popular smartphone app has several „privacy issues“ due to lack of encryption.
but there is an alternative solution with end to end encryption: Threema.
The company behind Threema is based in switzerland.
They have a special section within their FAQ for security questions: FAQ
Threema is at the moment only available for Android and iOS, so no Blackberry nor Windows Mobile support, but that should only be a question of time.
Another blogpost about threema: http://damienclayton.co.za/2013/09/threema-secure-mobile-messaging-for-everyone/
But there are some concerns as the messages are stored plain on the device: article on hetzel.net (german only)