Misc. Dialplan Tools speak
From FreeSWITCH Wiki
Speaks a string or file of text to the channel using the defined speech engine.
Flite is a free TTS engine that isn't suitable for production environments but is very handy for testing TTS applications during the build phase. Flite has these voices:
<action application="speak" data="flite|kal|FreeSWITCH is awesome"/>