Text-to-speech (TTS) is a form of speech synthesis that converts text into spoken voice. Text-to-speech is an easy method to add dynamic voice to your phone capabilities. Unlike pre-recorded audio, this feature can be used to deliver spoken versions of text such as live information (e.g., sports scores) and other dynamic messages (e.g., emergency updates). Examples of simple changes in the code can allow you to change the message, the voice (e.g., male or female), who will be receiving your message, and much more.
For more details, refer to https://www.plivo.com/docs/getting-started/text-to-speech-on-a-call/