Square Wallet app adds gift cards Square, the San Francisco mobile-payments startup, is giving small merchants the ability to sell gift cards to shoppers on the go, stepping up competition with eBay's PayPal business. A new version of the Square Wallet app, which works with Apple's iPhone and iPad as well as devices running Google's software, lets users buy and redeem gift certificates in amounts from $10 to $1,000. Recipients of Square's cards can integrate them into Apple's Passbook app, which stores loyalty gift cards, digital tickets to movies, concerts and sporting events in one place. Square also announced plans to process transactions in Starbucks stores, an agreement that included a $25 million investment from the retailer and added the coffee chain's chief executive officer, Howard Schultz, to Square's board.