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).
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).