You already can pretty much. Imagine publishing do iPhone version of all their mags. You d/l the app for the particular mag and it throws in the current edition of the e-mag 'for free'. Then you can buy later editions of the mag (for about half the price of the paper version) or take out subscriptions using in-app purchasing. They've said they will allow people a free upgrade to the iPad version of the app which is already in production. The mag viewer works a lot like viewing a PDF file - flip pages with gestures, pinch to zoom in to read part of a page etc.
Have a look on the app store for 'pixel mags' - that the company that develops the viewer app they use. There's a wide range of mags there.
Future publishing have also hinted about doing something with the iPad, although I haven't seen anything concrete yet.
I'd much prefer e-mags actually. Save the planet and all that. However I'd probably prefer them to be ebooks, assuming we get the 'IBooks' application even if we don't get the bookshop immediately.
