The features and functions of mobile apps are overkill for most mobile moments. By contrast, messaging rightsizes customer engagement through a combination of notifications and conversations in the form of text, sounds, images, videos, links, forms, and more. Engaging customers through messaging demands a technology stack that is connected to, yet distinct from, systems that support mobile apps or mobile sites. This report defines the eight types of mobile messaging vendors available to digital business professionals and how their capabilities differ.