WoW - D3 friends

[Radeghost]

Hi.
I've got a question regarding Friends in Diablo 3 and in WoW. If I have Diablo 3 and my friend doesn't, that means it's impossible for him to add me on Friends by using battletag?
Or will it be possible just by Real ID? Because some of my friends that I'm contacting via RealID don't have diablo 3 and I don't know how is it possible for me or them to contact me from WoW while I'm playing D3.

[Deleted]

You can have contact with people on your real ID across all current blizzard games (Diablo 3, World of Warcraft and Starcraft 2)

[Radeghost]

So they don't need to add my BattleTag, or the BattleTag comes up with RealID?