I have been interested in computing from cell phones and PDAs for a while. I think the reader device of choice will be the cell phone. Not because it is the best, but because it is the most convenient. People are already reading vast quantities of text from their cell phones via texting and in some cases e-mail. But phones like the iPhone, with reasonable browsers are making reading even more from that little screen a real option for more and more people.
Now OCLC is in the game -- see http://www.worldcat.org/m/ for WorldCat from your cell phone. If your phone has GPS capabilities (like the iPhone) then it will even show the library closest to you that owns the book. Olin Library really needs to make a mobile friendly version of its website. Like the Washington Post for example, which is my current favorite phone reading site.
Other vendors, like ProQuest and SerialsSolutions are talking about this, but I see no evidence of progress yet. Our students should be able to download fulltext on to their cell phones, or send records via text message or otherwise to their phones. From our catalogs they should be able to download a record to their phone (or search the OPAC directly from their phone) and then wander the aisles of the stacks until their phone beeps when they are close to the location of the book. they should be able to access a database via their phone from the classroom and share the results with other phone users in the class.