Grammar Server is a product they make for building and managing speech recognition grammars. It's pretty awesome, too, and any recognition grammars you create can be used with Tropo.
Disclaimer: I'm one of Nu echo's founders and lead architect for our IVR testing and monitoring tool suite (NuBot and Mirador).
Thanks Adam,
That is surely yet another point in favor of Tropo. They test. Using our NuBot Platform, we have load test their infrastructure with several concurrent calls. A few issues came up and Voxeo promptly fixed the issues. Case closed. Tremendous support.
I don't know about Twilio in such regard. A few months back, I have offered Twilio our load testing services but I haven't heard of them so far. Danielle, Jeff, if you read this, drop me a note (pdeschen @ nuecho dot com) and we'll be pleased to load test your infra! :-)
NuBot is the IVR testing product http://www.nuecho.com/content/view/28/147
I'm not sure of the cloud per minute pricing, but they'll likely be pretty responsive on email. They're a good group of people.