source and the whole story:A character can only be transferred to a new realm once every six months, and once completed, a character transfer cannot be reversed. Also, there will be both character and realm restrictions. For example, you will need to be at least level 10 to transfer realms, and you'll only be able to carry over a certain amount of gold. The cap is set at 300 gold for characters between levels 10 and 30, 1,000 gold for characters between levels 31 and 50, and characters at level 51 and above can bring a maximum of 5,000 gold.
As for realm restrictions, players can only transfer characters between realms of the same type, or from a PvP to a normal (PvE) realm. To prevent players from leveling up without the challenges of a PvP environment and then unfairly being able to make leveling up more difficult for other players on a PvP realm, transfers from a normal to a PvP realm are not permitted. Also, if a player decides to transfer from one PvP realm to another PvP realm, he/she can only do so if there is no faction violation (that is, players cannot already have a character of the opposing faction on the destination realm).
Most of the restrictions we have in place are to prevent abuse of the service, and we don't feel they will impact regular players.
http://www.gamespot.com/news/6153087.html
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[UPDATE]: A Blizzard representative confirmed for GameSpot that realm-transfer capabilities will be offered to European players, as well, with details to be announced in the near future.
