That will get you a cell in the UK, true or not.

In the US, it will probably get you denied entry, possibly permanently, for "lying to a customs officer" (if a non-citizen), or the device possibly being confiscated if you're a citizen, (and a note in a file somewhere that says you've probably lied to a federal agent — particularly if they happen to catch any security camera footage of you stupidly using your device shortly after exiting the international arrivals area).