From Em Software:
Why doesn't InDesign automatically add pages when I have overset text? Scratching your head over this question? (We are.) InFlow is the answer. InFlow is great news for all of you who, like us, love using InDesign but can't live without automatic page insertion. Now you can turn any master-page text thread into an autoflow text thread in about 3 seconds. When InFlow detects overset text, it creates a new document page (instead of making you do it) and links the current text story to the autoflow text threads on the newly-created page so that text can flow automatically (instead of making you do it). Just like you expect, right? InFlow can automatically flow placed text, typed text, or text generated by other plug-ins, such as our own InData and InCatalog for which it was originally created (and with which it's bundled). And as a bonus, you no longer need to hold down special keys to activate InDesign's very limited autoflow capabilities when placing text - just click the loaded cursor on an autoflow frame and let InFlow do the work.