"First, tell the caller to do this...."

There's nothing that demonstrates the differences in assumptions between VUI designers and IT or business people than the way they express their ideas for how prompts should be written.

• "First, tell the caller to do this. Then tell them to do that. Then, they'll pick this option and they'll be where they should be."

That's IT/business speak. "Telling" callers to do things over the phone is a losing proposition. Assuming that they'll follow your cryptic commands isn't reasonable. Usually, they aren't your subordinates, and even if they are they usually aren't compelled to follow your instructions. In fact, you're often dealing with customers who may have the funny idea that YOU should be responsive to THEM.

The assumption that you can tell callers what to do leads to a logical fallacy.

• If callers obey instruction n they'll obey instruction n + 1.

This leads IT/business types to propose endlessly long dialogs, another assumption being that the caller on the other end of the line has no alternative but to obey instructions. VUI designers know that's not how people operate. At each step in the dialog callers evaluate whether they're getting closer to their goal, and whether it makes more sense to press the magic zero key (or say "agent," or play possum, or press the pound key three times, etc). People aren't calling to make the company's life easier, they're calling to get something--and that thing may be something they've already paid for and you owe them.

You can present the business people with call statistics that show you lose a percentage of callers on every question asked in a dialog, but often the message doesn't sink in. It's a matter of assumptions, and getting people to change unvoiced assumptions is a difficult thing indeed.