Wrocas (European community manager) announced on the WoW forums moments ago that a guild chat feature will be added to the Mobile Armory that's available on both the iPhone and Android. Players have been asking for this type of feature ever since the armory was introduced. This feature piggybacks off the same service that the remote auction house uses, which requires an additional monthly fee on top of your normal World of Warcraft subscription. One fee to rule them all (and by "all," I mean both the mobile auction house and the guild chat feature).
This allows access to guild chat, officer chat (presuming you had access to start with) and whispers. It appears the whispers will only be allowed to and from guild members, at the moment. There is also no news about being able to chat with your Real ID friends. If you don't have a device that the Mobile Armory runs on, Blizzard will soon be adding this feature to the normal armory as well.
The full announcement is behind the break.
We're pleased to announce a new feature being added to the Mobile Armory: Guild Chat!
Coming soon in an update to the Mobile Armory app available in the iTunes App Store (http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=321057000&mt=8) and Android Market, this new feature will allow all World of Warcraft Remote subscribers the ability to chat with their guildies right from their mobile device. Access to the guild chat feature is included for no extra charge in the €2.99 World of Warcraft Remote Auction House (http://eu.wowarmory.com/wow-remote.xml) premium monthly subscription. In addition, soon after the launch of the mobile version we're planning on adding the ability for premium subscribers to use Guild Chat through any browser on the Armory website.
Guild Chat will allow you to chat with your guildmates via Guild Chat, Officer Chat, and Whispers. Now you can stay connected with your guild or update them from anywhere if you're going to be late to a raid! Stay tuned for additional information about this service and the upcoming Mobile Armory Guild Chat beta test.