A-SIT has published a survey paper regarding the security of current smartphone platforms. Currently the survey is available in German only.
However for detailled information about encryption systems on mobile platforms, you can consult the following publications of A-SIT:
iOS Encryption Systems – Deploying iOS Devices in Security-Critical Environments, SECRYPT 2013 (EN, PDF)
Peter Teufl, Thomas Zefferer, Christof Stromberger, Christoph Hechenblaikner
Android Encryption Systems, PRISMS 2014 (EN, PDF)
Peter Teufl, Andreas Gregor Fitzek, Daniel Hein, Alexander Marsalek, Alexander Oprisnik, Thomas Zefferer