This advice makes sense given the threat model. However, it might not make sense for someone in Edward Snowden's role. If I were a military agency with a big budget, I would backdoor the shit out of every phone, enforce cultures of secrecy inside companies like google, apple, facebook, intel, qualcomm, at&t, and off any executive that interfered with the mission. Then I would pay experts to spend their lives on internet forums asserting that devices with two cameras, two microphones, wifi that can function as radar, an unremovable battery, a closed-source operating system and root access only available to a major US corporation via ssh, are the most secure computing platforms in the universe. That's just me though, if I had a lot of money and lust for world domination, neither of which I possess :)<p>Edit: removed sentence "Most mobile devices have baseband chips with DMA"