The two companies have collaborated to offer Intuit GoPayment for AT&T, a mobile application and credit card reader that helps small businesses process credit or debit card payments using their smartphone or tablet.

Available via AT&T's nationwide small business sales force and call centres, the reader comes with automatic signup and pre-approval for the majority of AT&T customers.

According to the Yankee Group's 2011 Mobile Money Forecast, the value of mobile transactions worldwide will grow from $241 billion in 2011 to more than $1 trillion by 2015, a compound annual growth rate of 56 percent.

More than 800,000 businesses use Square's small white plastic cube credit and debit card reader, which plugs into the headphone jacks of mobile phones and tablets to perform transactions. The company has been growing at an explosive rate and is now valued at $1 billion.

Intuit is aiming at the millions of small businesses that already use its financial accounting software by syncing GoPayment transactions directly with QuickBooks.

Like Square, the basic GoPayment service has no monthly, transaction or cancellation fees, and offers a 2.7% discount rate (2.75% at Square) for swiped transactions.

For small businesses with higher volume processing needs, a paid version of GoPayment also is available for $12.95 a month and provides a lower discount rate of 1.7% for swiped transactions.

This plan is recommended for businesses that process more than $1,000 a month, says Intuit, and want multiple employees to process payments using one GoPayment account.

The monthly fee for the paid version of GoPayment will be rolled into customers' existing monthly AT&T bill.

Chris Hylen, vice president and general manager of Intuit's Payment Solutions division, says: "By teaming up with AT&T, we're getting GoPayment into the hands of even more small businesses. Now they too can easily and affordably process credit cards and get paid on the spot, which in this tough economy means increased cash flow and more repeat business."