The Kindle version has been available for some time at amazon.com. Now, Adobe ePub and MobiPocket versions are available from BooksOnBoard.com for $7.88.
It’s my understanding that ePub books can be read by the iPad, Nook, Sony Reader, and other devices. The Mobi format is supposedly supported by Palm, Blackberry and other smartphones, as well as by the MobiPocket reader.
I’m not an expert on reader formats, but you can check with BooksOnBoard to confirm. As reported earlier, a number of eBook formats should be available within the next few weeks, and should be showing up on the appropriate sites soon.