At the moment we're focusing on iPhone, mainly because it makes things a lot easier to target such a consistent platform - if there's only one hardware maker then there's only one screen size / processor speed / camera resolution (if we ever get around to introducing a camera OCR system) / etc to deal with. Plus, with at least three different OSes competing to be #2 behind iPad in tablets, we think Apple is poised to continue dominating in that market at least for many years to come, and that's probably as big a part of Pleco's future as smartphones at this point - maybe even bigger if they catch on with schools.
Android is *incredibly* hard to port a product like Pleco to - too many different OS versions / hardware configurations, not to mention the need to rewrite everything in Java - and Windows Phone 7 hasn't proven itself in the market at all yet, so until the Android development situation stabilizes or Microsoft demonstrates consumers are actually buying WP7 we'll probably keep our focus on iPhone; the most likely second platform at this point is actually desktop Windows since that's an easy port from Windows Mobile.
Just wondering how hard it would be to port to Mac and if that's on your roadmap too? I don't really know much about programming - would that be a relatively straightforward port from iOs? As much as I'd like a desktop client, I try and avoid Windows like the plague. Fortunately I use Macs at home, school and work.
A Mac version is certainly a strong possibility if the Windows version is a success, but it's easier to port to Windows, and Windows is in some ways more important since it lets us reach out to the pretty sizable number of people who hate Apple and hence aren't likely to be interested in our iPhone/iPod/iPad software.