I went to the USA in August. I got a special phone and special computer pared down to the minimum for that exact reason, together with a server with an encrypted copy of the personal data I may need. I was not controlled at the border and generally belong to the class of people who should have nothing to hide, but did not want to take any risk.
If the customs officer would have asked why my phone had not data older than two months, I was prepared to say that I bought it for the occasion (which would have been true, actually). Smartphones are more useful on travel than at home, where I do not need maps, etc. Because of my age, that story would have been believable. A younger traveler would not have it so easy as the customs officers would probably not believe that they do not use Facebook, Whatsapp, etc… and could simply let him or her in prison till he or she gives the passwords to their social networks.