AT&T fulfilled its promise of nationwide mobile banking on Tuesday, rolling out a service for customers of two banks that uses an application residing on the user's handset.

Although Web-based online banking is widely used, mobile banking is still getting off the ground in the U.S. Some national banks, including Bank of America, already offer mobile banking services that customers can reach on their browsers. But the service AT&T will offer with Wachovia and SunTrust Banks uses software that will either come with the phone or be available for download. This approach will make it easier to find and use the banking feature, according to the carrier.

The software, based on technology from Firethorn Holdings, is available on the carrier's 3G (third-generation) high-speed data network as well as its national EDGE (Enhanced Data Rates for GSM Evolution) service. Wachovia has 13 million household and business customers around the U.S., according to its Web site. SunTrust has about 5 million household customers across the southeastern U.S. In March, AT&T announced it would offer the service with Wachovia in the third quarter and also started providing banking software on customer's phones for BancorpSouth, a regional bank.

Wachovia and SunTrust customers can check their account balances and activity and transfer funds on their phones, as well as pay bills. The software is designed to minimize the number of screens a user has to go through to find the banking system and get things done, according to AT&T.

The software can be downloaded and run on more than 30 handsets AT&T offers, which represents more than 30 million devices already in the market, the carrier said. Starting later this year, AT&T will preload the application on new handsets.

To use the service, customers have to sign up on the bank's Web site, which will issue a one-time initialization code to be entered on the phone. Then the user creates a PIN (personal identification number) to get into the banking application. All the traffic is encrypted, and subscribers can deactivate the service immediately if they lose their handsets. For additional security, they can only add new bill payees through the bank's Web site.

The banking service won't drive up subscribers' phone bills, according to AT&T: Charges for data usage will be minimal, the carrier said, though it recommends a data plan starting at $9.99 for customers who will use the service frequently.

In-Stat analyst David Chamberlain is surprised mobile banking isn't already widely adopted, given the popularity of online banking.

"It's one of those things that just seems like a very logical extension of what's being done right now," Chamberlain said.

Historically, consumers' biggest worries about mobile banking have been security and extra charges, Chamberlain said. AT&T's use of an application loaded on the phone should be more secure than the browser-based approach others have taken, particularly with the ability to turn off the feature if a phone is lost, he said.