If watching Kitchen Nightmare clips on YouTube has taught me anything, it’s that the menu dictates the success or failure of a restaurant almost as much as the location. There’s a lot of psychology built into menus, from anchoring of menu prices to ordering of wines. Too many choices typically leads to less satisfaction by the client when a decision is finally made.
For voice interaction, it makes sense to limit choice to take advantage of the interaction speed. Pizza ordering? Only one choice (last order) vs. a large menu of items. For product ordering through Amazon, the first selection is usually the one that the user wants, so offering it vs. a list of items is better.
The IVR tree is a legacy from green screen days when text menus were the norm. The choice for voice interaction should be unlimited selection through natural language (with verification of order) or one or two items.