Meanwhile you could use the waiting time effectively by downloading the demos and start learning how to add pitch & melody to a synthetic voice.

If you already have access to the voice, and a way to save it to a sound file then all you need is a Melodyne demo, available here:

http://www.celemony.com/cms/index.php?id=demos

this is a 30 day demo, almost as long as the wait for your dynavox.

If you don't have a way to convert typed text to audio speech then save it as an MP3, here's is a downloadable app that will let you do exactly that:

http://download.cnet.com/Text-Speaker/3000-7239_4-10877963.html

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0