The mobile device for the secure government set is now a "hardened" Samsung Galaxy S4.
When President Barack Obama took office in 2009, he pushed to keep his BlackBerry. Instead, he was issued another BlackBerry device—a BlackBerry 8830 World Edition with extra crypto—for unclassified calls and e-mail. Until recently, Obama continued to carry a BlackBerry handset, but mobile device technology shifts have finally caught up with the White House. Sadly, the Obamaberry is no more.
In an appearance on Late Night with Jimmy Fallon, Barack Obama noted that he now carries a secure "smartphone" that is so locked down that he compared it to an infant's toy phone. While Obama didn't mention the type of handset he now carries, there's only one mobile device supported by the Defense Information Systems Agency—the agency that provides the White House with communications services. That phone is a "hardened" Samsung Galaxy S4.

https://www.youtube.com/watch?v=aMcKi1TS2Zs

The S4 is currently the only device supported under DISA's DOD Mobility Classified Capability-Secret (DMCC-S) program. In 2014, a number of Samsung devices were the first to win approval from the National Security Agency under its National Information Assurance Partnership (NIAP) Commercial Solutions for Classified (CSfC) program—largely because of Samsung's KNOX security technology. And the S4, layered with services managed by DISA, is the first commercial phone to get approval to connect to the Secret classified DOD SIPRNet network.

DISA has been working with vendors and the National Security Agency's Information Assurance Directorate to develop a Top Secret-capable mobile device for use by the Defense Department and the national leadership both on the move and within secure facilities. But currently, the highest level of classification that can be handled by commercial devices under the DMCC program is at the Secret level. Secretary of State John Kerry was a DMCC-S early adopter, and he served as a beta tester of the hardened Galaxy S4.

The DMCC-S handset sacrifices some of the Galaxy's functionality for security purposes. While it uses biometric authentication, there's no user-accessible camera, so there's no selfie-snapping in secure facilities. The Android applications on the DMCC-S Galaxy are restricted to a selection from DISA's Mobile Application Store (MAS).

The stock DMCC-S Galaxy can be used for standard domestic and international calling as well as secure Voice over IP calls. E-mail access on DMCC-S devices is provided through "secure Outlook Web Access," according to DISA's data sheet for the phone. However, Obama's device appears to have even further restrictions for security purposes. Obama told Fallon that he can't place phone calls on it—the phone is likely restricted to secure VoIP functionality, with outside calls controlled from a secure switchboard.