Great post, I love your clean IVR design and thought process! A couple notes and ideas that I thought I’d offer:

1. In menu.xml, you don’t need separate blocks for each option, you could just as easily use For sales, press1. For service, press 2…. Your solution works as well, so maybe it’s just personal preference :)

2. If you have multiple exit paths, and keeping track of the failure-counter in the URLs is difficult, you can keep track of failures in a cookie instead! Twilio is a well-behaved HTTP client, so you can use cookies to track data across many pages. You can even use PHP sessions, etc.

Again, great post! Keep the awesome ideas coming.

-jeff