The list of places that you can pick up a Square credit card reader for your mobile device continues to grow, with the company announcing a new partnership with AT&T today. As part of the deal Square's readers will be available at over 1,000 AT&T retail stores throughout the United States, which according Square means that the readers are now sold at more than 20,000 stores across the country — including recent partners Walgreens, Staples, and FedEx. The card readers cost you $9.95 (with a $10 rebate once you sign-up for Square's service), and Square believes that its latest partnership will help it better reach small business owners. Overall it's been a busy summer for Square — earlier this month the company signed a deal with Starbucks, creating the largest mobile payment network in the US.