Mobile devices make ideal personal ambient information systems given their ubiquitous adoption by users and their rich context knowledge of users’ activity. However, we believe that unlike traditional systems, the mobile device acts more as an interstitial information appliance, allowing users to consume relevant information at-a-glance primarily during the interstices between other activities. In this paper, we motivate a discussion on how such usage behavior can impact the design, display and delivery characteristics of ambient information systems for mobile devices. We focus not just on design issues (information selection, rendering ions, impact evaluation) but also on the ecosystem concerns (provisioning costs, business models) that often prove critical to developing commercially-viable solutions. Keywords Ambient interfaces, mobile media, information awareness, presence, context-awareness