[Muromec]

It's a good advice if you are citizen and cant be compelled to unlock the phone or be denied entrance for not consenting to search.

The good opsec in general, I think, is to comply, not have an obvious burning phone setup, but to have nothing capturing attention

[lordofgibbons]

They can still hold you for a long time (days?) at the border without being formally charged with anything. That's what I've been told, not sure how true it is. A Canadian entering the U.S was held for 2 weeks with no charges - not just a entry denial.