If American banks were as smart as BMO/Bank of Montreal here in Canada, they would do what BMO did. Build an HTML5 based app. The Android, BB10, and iOS apps look and operate the same. No WP app since WP has virtually no marketshare here in Canada. However, the mobile website ALSO looks and operates nearly identical as the Android, BB10, and iOS. That is the most cost efficient way and "futureproofing" your mobile app.
Posted via the Windows Central App for Android on my BlackBerry Passport