The recently released Battle.net Desktop App now includes the ability to chat with your friends if they are logged on to that same app, or any of WoW, SCII, D3, Hearthstone, Heroes of the Storm or Overwatch.
Update: Some in game items are unavailable for gifting.
It is currently possible to gift: World of Warcraft, WoW mounts/pets, StarCraft 1/2, Warcraft 3+expansion, Diablo 2+expansion and Diablo 3+expansion.
Pre-purchase of Overwatch and WoW:Legion seems to not be giftable.
From the blizzard support page:
Gifting Items
Heroes of the Storm in-game items, and Hearthstone in-game items are currently unavailable to gift.
To gift an item, click Gift instead of Buy Now on the item’s page.
During checkout, enter your friend’s email address. Once we process
your purchase, we’ll send a key code to their email address, and
you’ll receive a purchase receipt at your registered Battle.net email
address.
Note: Gift processing may take a few hours. If you entered the wrong email address, you can find the key code for your purchase on
the Order History page once processing completes. You can copy this
code and send it to your friend.
Your friend must have a Battle.net account to claim a game key. If you
gift them a World of Warcraft pet, mount, item, or game time, they
must have a World of Warcraft licence in good standing (not banned or
suspended) attached to their Battle.net account.
Note: You cannot gift Battle.net Balance, World of Warcraft character services, guild services, or subscriptions.
Best Answer
First, Battle.net is divided into two completely separate and distinct partitions, known as Worldwide and China, each of which has completely separate accounts and game servers. There is no connection whatsoever between the two partitions. An account on one partition does not exist on the other.
A Battle.net account exists within a partition.
Within each partition are regions. The regions are game-specific and so different games may use different regions. An account may play the same game in multiple regions, but will have different characters, achievements, etc., in each region, which do not transfer between regions.
The China partition has only one region, CN. In the Worldwide partition, there are multiple regions:
An account may authenticate to any region in the partition, but still play games in a different region in the same partition. The only benefit to authenticating to a different region is the possibility of reducing the latency of the login process.
With all that out of the way:
In China, Blizzard (actually, the operator NetEase) is required to ask for players' National ID numbers. Everyone in mainland China has such a number, so it is mandatory to provide one if you register an account in the China partition. (However, the last time I checked, Blizzard doesn't actually verify these numbers with the government, nor does it check the validity of the ID.) Due to the unique state of Taiwan's political situation, it does not use the same system of NID as China. The same is true about Hong Kong and Macau, where both places have separate ID systems. As such, it is optional to provide the NID if you register an account in the Worldwide partition.