American consumers have been letting their fingers do the walking for a while now when it comes to banking online, and mobile banking helps make sure those fingers are sticky.

While that telcom slogan retreats into the yellowed pages of marketing history, comScore reports 81% of Americans over the age of 13 have a smartphone. But thousands of American credit unions still don't let their members bank on them. There appears to be a disconnect.

Mobile has been a mandate for many credit unions for the past few years, and the economics clearly show why. It's way more efficient than going into the branch. A Bain & Company report notes for every 100 mobile interactions there's an average decline of 16 branch transactions. That same report finds that frequent mobile users are 40% less likely to switch banks.