If you want to skip the lines at U.S. immigration and customs at some airports, all you need is your smartphone.
Mobile Passport is a free app that is available to iPhone and Android users in the Apple App store and Google Play store. After entering in your passport and travel information — which you can do while in the air and your phone is on “airplane mode” — into the app and then electronically submitting it, the app generates a receipt for you to pass through immigration checkpoints.
There are five airports where you can use Mobile Passport: Hartsfield–Jackson Atlanta International Airport, Miami International Airport, Seattle-Tacoma International Airport, Chicago O’Hare International Airport, and San Francisco International Airport.
The app is officially authorized by the U.S. Customs & Border Protection and is currently limited to U.S. and Canadian citizens with valid passports.