In this post, Devin Rader demonstrates how to add audio controls to the BasicPhone app using Twilio Client for iOS with Swift. The app now allows users to send input tones (DTMF tones) from the device microphone and control the audio output by muting the device microphone and swapping the audio output. The user can select a song to hear, and then toggle the speaker to play it through the built-in speaker and microphone. Additionally, the app includes a feature to mute the user's voice while on call, allowing them to speak into their computer microphone without being heard in the cell phone. The post concludes by highlighting potential future features for the app, such as sending parameters to Twilio from the iOS app, detecting network connectivity, and creating a more beautiful UI.