United Airlines is offering a new mobile app that allows select MileagePlus members to use their smartphones to pay for items at U.S. retailers while earning MileagePlus miles for the purchases. The app is in a trial phase before being rolled out to all MileagePlus members. The iOS and Android app allows users to browse for participating nearby retailers such as Lowe’s, Sears, GAP and AMC Theatres, and view the amount of miles they can earn on purchases when they enter the total they plan to spend. When inputting the dollar amount, the user will get an instant digital gift card that the cashier can the scan for the barcode, which will automatically sync to the user’s MileagePlus account, to get the miles instantly added to the account. In the future, the app will feature a way to pay with miles for in-store purchases.