Debtor version 1.5 is now available in the App Store.
The keyboard functionality has changed in this version to use the full keyboard instead of the number pad keyboard. This way, I was able to eliminate the need for an accessory bar above the keyboard with Navigation and a Done button. This frees up more space for content, which is needed on the iPhone 4S. The standard keyboard already has a Next/Done button. Plus, tapping anywhere in the background on the Calculation screen (the first screen in the app) will dismiss the keyboard!
Support has also been added for the new iPhone 6 and iPhone 6 Plus, and for iOS 8 as well. Feedback and reviews in the App Store are appreciated!