In an earlier post, I had predicted that Blizzard would be adding in-game chat features via mobile phone. (e.g. "A lot more mobile services definitely! The Remote/Mobile AH is just a start. Checking in-game mailboxes. Inventory, bank, character, and talent management through mobile. In-game chat with Guild, General Chat, Trade Chat, etc through mobile/remote.")
Looks like it was just revealed a couple days ago. Premium monthly subscribers (those who are paying an extra $3 per month) will have access to a new feature that allows them to communicate with Guild members while mobile.
How utterly.. predictable.