Square's been making waves in the mobile payment industry for the past year or so, but now it's taken a step forward and is making its iPhone and Android readers available in major retailers in the US. Twitter co-founder and Square CEO Jack Dorsey has announced via a tweet that the readers are now available in Apple Stores, Best Buy, Radioshack, Target, and Wal-Mart for around $9.99. The device makes it quicker and easier to use Square's card services by allowing the user to swipe their card rather than keying in numbers.