US customs on mail parcels cannot
1) compel you to unlock your device
2) threaten you with deportation for non-compliance
not to mention that there are rooms and people trained in every airport to scan your phone as a routine component of their daily function WHEREAS customs on mail are 90% concerned about duties and 10% concerned about smuggling. 0% on what kinda sms you send to your buddies
No but it gives them far more time to plug your phone into a device that dumps the device for decryption later, as well as attempting any kind of security backdoors/exploits, or even clone the SIM card.
not to mention that there are rooms and people trained in every airport to scan your phone as a routine component of their daily function WHEREAS customs on mail are 90% concerned about duties and 10% concerned about smuggling. 0% on what kinda sms you send to your buddies