ING Direct offers core banking functions, such as the ability to check an account balance via a mobile device, as well as the ability to pay a bill or to transfer funds to a friend from through a Person2Person address book. What is distinct is that ING Direct also built in social applications, such as Flip for Fun, which lets bank customers flip a smartphone sideways to enter ING's or pages or its "We, the Savers Blog."

About 80% of banks offer some form of mobile banking, according to Jupiter Research, and ING Direct feels that users' ability to quickly access to social apps will encourage more customers to use it.

Wolfs wouldn't divulge the exact cost of building the mobile banking and investing apps but said it was millions of dollars, with the majority spent on actual development efforts and maintenance of the apps rather than on the cost of the tools, which were provided by Antenna Software.

The mobile applications were conceived two years ago, but actual development took about four months. Antenna proved to be a good choice because it provided a core development environment called Antenna Mobility Platform (AMP), which enabled the building of mobile apps that could be delivered to multiple devices quickly and securely, Wolfs said. "We have the ability to write code once and deploy to many devices in a world of quickly changing devices," he said.

Antenna CEO Jim Hemmer said that in addition to providing a means for building apps that work on multiple devices and networks, AMP can support millions of mobile transactions per day. AMP also supports data compression, which reduces data consumption by up to 90%. Antenna supports security capabilities as well, including encryption and user authentication.