A few places are reporting, including our sister site Massively, that a company named Vollee has brought their mobile phone version of Second Life live and online. As you can see in the video on the website, it works, though it's not exactly an ideal way to play the game. They don't go into details on how it works, obviously, but my guess would be some kind of java browser emulation of a real client.
Why are we talking about Second Life on WoW Insider? Because odds are that some kind of mobile WoW app is not far behind. Vollee would certainly love to be the ones to do it (they even say that you can enter "World of Second Life" on their website), but unlike Blizzplanet, I really don't think they will be -- odds are that any mobile app won't be a full client, but rather will be a chat or AH app of some kind ("BattleChat" has already been mentioned by Blizzard), and it'll likely be designed by Blizzard themselves.
But there's no question that there's a huge frontier for this sort of thing. Within the next month, Apple is set to release the iPhone's "App Store" (a distribution platform for mobile applications and games), and we have to imagine that a mobile announcement or even a release from Blizzard will come soon after that.