The Programmable Voice Guide, written by Devin Rader for Twilio, provides information on three key topics: gathering input during a call, recording calls, and modifying in-progress calls. The guide shows how to use the `<Gather>` verb to collect caller input, the `<Record>` verb to record calls until a specified time or key is pressed, and how to modify an in-progress call using the REST API and Twilio's Ruby helper library. These features enable developers to create dynamic experiences for callers, such as IVR systems and custom voicemail systems, and can be used to improve customer support and feedback processes.