CNET has found out which phones have been sealed up tightly enough to satisfy the NSA's guidelines for devices that may transmit data that's classified as "Secret." They're both quite similar, and kind of cool in a completely overdone way. Take the Sectera Edge. Underneath a modifed version of WinMo 6.1, you'll find a comically large set of unusual features, including GSM and CDMA network compatibility, "Classified" USB and serial ports and a secondary "trusted" display.
The L-3 Guardian is a slightly newer counterpart to the Edge, but with a worldlier bent and sleeker profile. Both phones were spawned from the Defense Department's Secure Mobile Environment Portable Electronic Device project, which was apparently intended to create an OS that allowed for private sector individuals to easily transition from their smartphones (BlackBerrys included) to an appropriately secured device. Such a device would be pretty well bolted down, so Obama will probably spend most of his presidency stuck, hilariously, trying to get Mobile IE to properly render his "Top Secret" national security briefs.
The security of the devices in question may not matter though, as the main reason for the push for Obama to relinquish his phone has to do with laws about record-keeping and privacy. As it stands, it looks unlikely that Obama will be able to keep any kind of smartphone, but the prospect of an unsecured BlackBerry seems almost impossible. [CNET]