If you are a player from the Oceanic or SEA regions and are currently using the NA client (enUS), Global Play is not yet enabled and you will not be able to switch to SEA. You will need to have the Oceanic/SEA client (enSG) installed in order to access the region change button and switch over to SEA to enter that region.

To download the enSG client, visit Battle.net Games Management page and download the English SG game client: http://oi45.tinypic.com/iwpyjq.jpg

For users that do have an enSG client, make sure you back one step out of login by clicking the arrow next to your saved acct name to switch to SEA.
Edited by Machkhan on 3/11/2013 8:39 AM PDT