What Nakedplumber said. I have spoken to a GM a few months ago and he said they are implementing cross server heirloom mailing soon (which I'm guessing will be in MoP). It's taking a while for them to do this because they have to "completely overhaul how the current mailing system works" (the GM's exact words).
Blizzard also said they might make heirlooms built into your account in some way so you don't have to mail them. Right now we really don't know what will happen with heirlooms. We'll just have to wait and see.
Blizzard also said they might make heirlooms built into your account in some way so you don't have to mail them. Right now we really don't know what will happen with heirlooms. We'll just have to wait and see.