Wireless carrier T-Mobile USA announced it will offer Square's credit card readers in select retail stores.

"The success of our small business customers is important to us," said Matt Millen, vice president of small and medium business sales at T-Mobile, in the announcment. "Formerly 'cash only' small businesses can now simply and cost-effectively accept credit cards with their smartphone using Square, giving them an easy path to growth." 

T-Mobile said it's the first wireless carrier to offer Square credit card readers in stores. The reader has been available at retailers like Walmart and Best Buy since last year. 

Square's mobile POS is aimed at giving small merchants who work in the field the ability to accept credit cards using their smartphones. The app, when coupled with the credit card reading dongle, turns iOS and Android devices into credit card terminals. The company recently announced it had signed 1 million small business customers.

For more stories like this, visit the POS research center.