Enhancing player experience in MMORPGs with mobile features by Elina M.I. Koivisto and Christian Wenninger is a paper presented at DIGRA 2005 that addresses how the massive multiplayer game experience could be augmented through mobile services. Although written in 2005, not much has really change concerning the cross-platform issues described in this paper, so it's still very pertinent. The paper interestingly provides the reader with a categorization based on "how the player can interact with or influence the virtual game world and other players by using his mobile phone. It's actually obtained through focus groups conducted both in Helsinki and in a virtual chat-room. The results they describe concerns:

Communication access: through IM or voice communication.
Event notifications: to be aware of specific events, some level of control is needed here, given that it could be intrusive.
Asynchronous gameplay: to manage specific game feature asynchronously, like crafting, mobile auction.
Synchronous player-to-player interaction, which may allow the mix of players using different platforms, through articial intelligence, especially in turn or tick-based game.
Passive participation: observe the game world or influence the game by voting or rating with the mobile device.
Parallel reality: "Real-life events can have an effect on the events in the virtual game world and vice versa", like location-based games.

It's also relevant that the authors describe how these feature would change (or not) the game mechanics. The factors that limit the mobile-enhancement are also mentioned and revolves around the problems of latency and I/O issue (text) as well as pricing for data transfer. This last point might eventually be fixed soon through flat fees. Why do I blog this? this classification emerged from focus groups is great material to be included in the literature review for a research project about this topic. Also, it allows to set some baseline about the current ideas concerning cross-platform gaming. There is a "physical" axis here which ranges from basic observation (gamer as spectator) to using real-life events in the game mechanic. I am convinced that other axes should be found to map more design opportunities.