CUPERTINO, CA - Apple stores have begun selling Square card readers, which enable iPhone users to make credit card transactions with their mobile phone, PC Magazine reports.

The $9.95 reader plugs into an iPhone, iPod touch or iPad and allows users (coupled with Square??s free mobile app) to process a credit card transaction, incurring a flat 2.75 percent transaction fee (credit card numbers can be input manually, too, resulting in a slightly higher fee).

Launched in May 2010 by Twitter co-founder Jack Dorsey, Square was formally launched for iOS and Android devices, but until now, neither has formally endorsed the product.

The move highlights the movement toward mobile payments, with the credit card companies, mobile carriers, Google and others all aggressively angling for a stake in the quickly developing payments landscape.

For more on mobile payments, be on the lookout for the cover story in the May issue of NACS Magazine, as well as a feature on Square card readers for iPads.