The CallMeBot API is very easy to use. You just need to GET the following URL using any command-line web browser such as wget or curl

http://api.callmebot.com/start.php?user=@user&text=This is Home Assistant calling to you to inform you about something that is happening at your house&lang=es-ES-Standard-A

Where user is your Telegram Alias or you can also use your phone number including the international code.
Text, is the message that you want the bot to speak.
And lang should be the language/voice that you want the bot to speak. You can get the list of languages here. Use the “Voice Name” as parameter to use. Please note that only the Standard languages are supported. (Wavenet premium languages/voices  won’t work with this API)

For example, calling to @myaliasname and speak the message in English with a Male voice:

wget ‘http://api.callmebot.com/start.php?user=@myaliasname&text=This is Home Assistant calling to you to inform you about something that is happening at your house&lang=en-GB-Standard-B

For example, calling to +34 123 123 1123 and speak the message in Spanish:

wget ‘http://api.callmebot.com/start.php?user=+33 123 123 1123&text=Este es Home Assistant llamando para informar sobre algo que esta sucediendo en tu casa&lang=es-ES-Standard-A