Remote Auction House
Update: The new auction house has the ability for you to use Guild Chat, but not much else as you can't go into individual channels or private chats. What it does have are 3D models so you can go around flaunting your gear.
What you can use it for is to get into a sniping or relisting war with other people if your phone has 3G or wifi access. If you're on the subways, trains or buses you can just log on and undercut to your glee or rebid against another.
Don't worry if you are using an authenticator, you can use the auction house app to pull it automatically from the iphone that you are using. You do however have to re-enter your password for each session of the armory.
After using the remote auction house on the iphone for quite a few days I have come to certain running observations and comments about the remote AH application on the itunes app store. I have as yet to use the web armory version of AH, but only the iphone, so this commentary would be thus limited only to the phone application and usage!
Firstly the observation that has to be said is that it is rather hard to dual wield the iphone and your local desktop or laptop WoW client at the same time. This is because if you are logged into WoW on a character, you would be unable to list auctions on it from your phone. This makes for some dull periods where you are waiting for a pull, and perhaps you're crafting some tailored goods in the downtime where your raid is recovering and drinking, but you would not be able to collect or list things onto the auction house.
This might be annoying as the purpose of the phone is simply to maximize your gameplay time into a shorter span while doing more. That is a trade of a tiny bit of money to maximize more time, as time is an expense and is expensive, and is worth more than the 2.99. So long as the armory auction house is in beta, and is thus free, there is little to complain about it though! Just know that until they decide to fix it or change their policies this is what you would have to live with.
There is however certain things you can still do in the scenario mentioned above, with your main logged into the game, but you have a phone running the remote auction house. Here are some definite things you can do to cut down on time spent.
If you regularly play on another server too, then this is easiest as you can zone in onto the other server's character and play the auction house. If you have a good steady mule or an alt in on the making gold game you can also pump items out onto the auction house from that very alt. Finally if you have none of these you can simply scan the auction house for deals, and sneak off to place a bid if needed.