Not only are more banks offering mobile banking, more are also releasing multiple applications to try to appeal to as many types of banking customers as possible.

The primary benefit of a fragmented approach is speed-to-market. Bankers say that if they're the first to offer a new feature, they'll have an advantage over their competitors. Building a new app from scratch can in many cases be faster than integrating a new feature into an existing one.

In the long run, though, having an app for every function is likely to cause mobile fatigue for customers and create major technology maintenance headaches for banks. "Having multiple separate apps, whether it's for different lines of business or different functions or features, certainly adds to consumer confusion and … the last thing we need right now in the mobile space is more confusion," says Emmett Higdon, principal of the banking technology consulting firm Prizm Strategy in Charlotte, N.C.

In many cases, banks are trying to meet an expected surge in demand for mobile financial services. By 2015, 50.6 million U.S. adults are expected to be using mobile banking services, up from 10.3 million in 2009, according to a report released in January by Forrester Research Inc.

However, for financial institutions, the benefits of investing in mobile banking are uncertain. In a separate report released in May, Forrester calculated that the return on investment in mobile banking is 15.7%, based on a hypothetical U.S. bank with 500,000 retail deposit customers and an average mobile banking adoption rate of 16%.

Returns diminish for smaller banks. A hypothetical bank with 250,000 retail customers would lose money with an ROI of minus-13%, the report said. Some smaller banks have released separate apps for reviewing transactions and for making deposits.

Citigroup Inc. last week released an application for the iPhone, iPod Touch and Android devices that lets customers in its ThankYou Rewards program redeem their points for in-store and online purchases from Best Buy. The application is separate from an existing app that customers with Apple Inc.'s iPhone or phones running Google Inc.'s Android operating system can use to view their account balances, transfer money between accounts, pay bills and other activities.

"This was the optimal way to do it" because it allowed Citi to release a feature in a reasonable amount of time and conform "to all standards on security and performance," Ralph Andretta, the head of loyalty and new product development for cards at Citi, said in an interview last week.

"We're integrating mobile solutions where it makes sense, such as our iPad app, which now includes the ability to manage card accounts, and also offering unique tools to address customers' distinct needs," Tracey Weber, Citi's head of Internet and mobile banking for North America consumer banking, said in an email provided by a spokeswoman.

Releasing the function in a stand-alone app may help it gain more attention from potential users and make it easier to find within mobile app stores, says Paul Grill, a partner with First Annapolis Consulting in Linthicum, Md.

In time, Citi may merge the rewards functions with its main mobile banking app, says Andy Schmidt, a research director with the TowerGroup research firm in Needham, Mass. "Otherwise, you're just adding hassles to the consumer," Schmidt says.