Regarding side-by-side portrait-orientation split views on the iPad, wouldn't such a layout require the message view to be too small? I'd rather that the message list appear in the top half of the screen, with the message view below it, but this isn't quite typical on the iPad (notable exception provided by Matt Gemmell's open-source MGSplitViewController [1]).

[1] http://mattgemmell.com/2010/07/31/mgsplitviewcontroller-for-...