Doug Read built a wedding guest book application using the Twilio Voice API, allowing guests to call in and leave messages that are then displayed on the website, with features such as transcription and playback of audio recordings, and integration with Google App Engine. The development process was made easier by Twilio's documentation and API libraries, but was hindered by the lack of a testable development environment. Doug plans to build more applications in the future, including home automation integration, and offers advice for other developers to play around with working example programs and utilize the debugger under their account.