"Infinite Text-In-Progress" relies on the fact that blinking dots appear when someone is writing an iMessage reply to someone else. To be precise, this isn't "really" a text or SMS message; it's an iMessage.
At any rate, to pull the prank you don't even need an app. You simply send an animated GIF showing those blinking doets to the other person and send it to them via the iOS Messages app. Then, they will think you are typing -- for hours, if they are patient.
Notably, as pointed out in the comments of the story, although this is hilarious, not all versions of iOS and not all iPhones will support it. Shades of Android fragmentation.
For one, the dots aren't animated on iOS 6, just 7. In addition, some versions of the phone won't show blinking dots, even on iOS 7, as one commenter noted. His iPhone 4 doesn't display blinking dots, either, even on Apple's latest version of its mobile platform.
Although Android doesn't have iMessage, it does have several chat apps that support similar functionality. We'd love to see someone adapt this iOS prank for Android.
After all, Android users deserve some fun, too.