I built such a dialog box for my CommandFusion based systems. Command fusion is a system very similar to the Pronto Professional system. There are two parts; the System designer (think Pep2) and a run time package that runs on IOS devices and Android devices. I run mine on iPads and iPhones.

The Dialog system is in two parts, a screen that is a subscreen of every page screen and is simply a nice box with places where the second part can place things like text and buttons. The second part is a Javascript function that does all the work. It is called whenever the dialog box needs to go up on a page. It makes the dialog box visible on the page (centering it), dynamically fills in the text, and sets up to 3 buttons with a limited set of names

If you PM me I will send you the two parts.  The javascrip[t code will give you some idea on what is involved.  I will answer questions, or read it over and call me and I'll walk you through the code