I tried few free online tools and found this site http://www.fromtexttospeech.com/ for free text to speech conversion because it's generated audios looks quite close to actual voice.
So I tried "Thank you for calling A T and T. How may I help you?" as sample text, and got this audio file generated with Alice voice.
Another audio file with Daisy voice seems similar to Google's voice.
So I think we can use this tool to generate customised audio messages. Now we need to focus what messages we need to put.
Note: Try the text in phonetic form to make sure correct pronunciation.