This was a highly-constrained environment, and not all of it was the regulatory and legal requirements of being a bank. A vendor did all the development on a home-grown hybrid platform with few capabilities and minimal ability to use native OS features.
Much of the process had to use existing components like these, with clunky pagination or needless popups. And lots of typing.
I was occasionally able to push things a little, like this. Aside from the needless difficulty of typing, there were so many constrains on amounts (steps, upper and lower limits) for this input that I was able to develop this selector.
Unfortunately, I was not able to get actual user testing, but to try to make sure that this was the right widget, I went to my patterns and found all the others that could be used. I put screenshots of them all onto handsets, and passed them around the department. I personally think the UI Picker (spinner, you might say) was the best answer, but by popular opinion the volume control slider thing was implemented.
These projects were implemented on every likely platform. All the smartphones, the mobile Web, and even a version for especially low-end mobile browsers.
Every platform. It even works in SMS response, so any device can get at least basic functionality.