Tome of Cold Weather Flying

Yup! You can mail Bind on Account items (including heirlooms like the Tome of Cold Weather Flight) to other characters on your account even if they're not of the same faction. The process isn't much different, either. Just open up the mailing window, drop in the BoA item into one of the available slots, enter the recipient's name, and hit "send."

One caveat: since the in-game mailing system is being used to actually complete the item transfer, the cross-faction characters (sender and recipient) will still need to be on the same realm. For now, at least.

Hm. It looks like a few of you may have missed out on an earlier Twitter Developer Chat, so here's a quick snippet:

Q u o t e:

Q. Are there any plans to implement cross-faction/cross-realm mail(for BoA gear and such)?
A. We have cross-faction mail for BoA items now; cross-realm is a work in progress, but we hope to have it done “soon."

Link: http://forums.worldofwarcraft.com/thread.html?topicId=23425524394&sid=1&pageNo=1#19