The Remote Auction House is a feature for Wold of Warcraft that will allow you to access the Auction House from an iPhone and from the web. This means that you can buy/sell items and do all your Auction House things without being logged in to World of Warcraft.
Currently this feature is in open beta testing. If you want to try out the Remote Auction House by using a web browser go here. The iPhone version of this feature can be downloaded here. Also there will be a limit on the number of transactions a player can do. The beta has a limit of 25 transactions a day but the live service will have a 200 transaction limit per day.
The Remote Auction House feature will cost $2.99 a month once beta testing is finished. More info about this feature can be found by reading this FAQ.