[mikeash]

If you are a US citizen entering the US (don't try this if you're a green card holder or a visitor), then in the case of (3), they can't hold you indefinitely, although they can hold your phone indefinitely.

This has never happened to me, and it probably never will, but if it does my plan is to refuse to unlock the phone and wait it out.

[crispyambulance]

I used the term "indefinitely" too loosely. I should have said "far longer than most people are willing tolerate for the sake of making a point."

But OK, staying locked is a fine thing to do but most people would want to get on with their lives.

[tony101]

Exactly. U.S. Customs and Border Patrol can't detain U.S. citizens indefinitely without charging them with a crime and trying them in court.