Category: 
Did I mention that I am a Certified VoiceXML Application Developer?
Well… I just did. 
Voxeo is the best place for developers to learn and test voice applications.
Tellme Studios and Voxeo have very good tutorials that can help prepare for the Certification exam. Of the two, I would say that Tellme Studios would be more helpful for the certification exam. Voxeo has more fun tutorials with a lot of humor and links to images which helps to keep you awake, without resorting to caffeine.
Another extremely useful resource is w3c, but it is also extremely boring.
To sign up for the test you can go to voicexmlguide.org.
Here is the list of certified developers:
http://www.voicexml.org/certification/cert_developers.asp.
Voxpilot seems to have a decent looking GUI grammar tool. But the grammar is easy enough to not use it.
Another helpful tool for designing voice applications is the late Vocomo Voice Studio. But I guess they went bankrupt and Voxeo has taken over - their support, sales and enhancements. 
