With patch 2.0.5 Global play is now active.
GENERAL Global Play is now live. - Players can now easily switch between regions via the new “Regions” button on the StarCraft II login screen. - Your game language and user interface will not change when you change regions. - Your character profiles and ladder data are unique to each region. - When your region’s game servers are undergoing maintenance, you may be able to play in a different region that is not down for maintenance. - For more information, please visit our Global Play FAQ on our support site.
Source: http://us.battle.net/sc2/en/blog/8953698/StarCraft_II_Wings_of_Liberty_Patch_205_Notes-3_5_2013
would be nice to play with people in both EU and Korea...