Original announcement: http://forums.wow-europe.com/thread.html?topicId=5640394530&sid=1

The free character migration to allow players on Molten Core, Shadowmoon, Stonemaul and Warsong to join larger realm communities has been opened. The destination realms for each are the following:

Molten Core --> Burning Steppes, Deathwing, Dentarg
Shadowmoon --> Boulderfist, Spinebreaker, Xavius
Stonemaul --> Ahn'Qiraj, Burning Blade, Jaedenar
Warsong --> Auchindoun, Bladefist, Haomarush

Note that each source realm has a destination realm in the same Battlegroup, underlined above.

These migrations will remain open until further notice, and at least until the release of the next patch. When the migration closes, remaining characters will be automatically transferred to the one of their destination realms with the lowest population.

If you have any questions concerning the closing of these realms, or the related migrations, please feel free to post them below and we'll do our very best to answer them. To make sure questions and answers are easier to find, any unrelated posts will be deleted from the thread.

Q: Why these destination realms? Why not Realm X or Y?
A: The realms were chosen based on several considerations; faction balance, overall population, and Battlegroups - each source realm was given a destination in their own Battlegroup. While arguments can be made for other realms, we felt these were the ones providing the best options overall.

Q: Couldn't you just have merged the four realms?
A: Even with merging the four realms the resulting population would be well below that of other realms, thus while it was looked at it was not considered a viable option.

Q: Can't you open free migration to all other realms?
A: We wish to make it an easier transition for players to move to a new realm by seeing at least some familiar player and guild names around, plus make sure it's easier for guilds and friends to easily agree on a realm and make sure everybody goes to the same realm. We also don't wish to stop this specific migration prematurely, hence we've picked realms that all can fit the entire population of any source realm. Additionally, there are technical limitations on the number of migrations we can have set up at one time.