On the Nook you'll be able to "side-load" your content and manually enter your Name and CC number for each book so that you can read them all on the device. My only concern is whether you can input this info when you install the book, or if you'll have to remember this information when you open it on the Nook. Once installed, I'd prefer I could open it at will.
Either way, the Nook will handle all sources. The iPhone stands alone for being a bit draconian.