Bangkok: I bought a SIM card in the 7-11 located on the walkway between the Intl Terminal and the Domestic Terminal. Minimum 150-300 baht. Can buy at any convienience store.
Taipei: you need a passport to purchase a prepaid sim card. You can go to any cell phone company office. They do have some located in the airport. 300NT minimum.
Malaysia: Can purchase prepaid SIM cards with a quick trip to a Cell Phone shop or Camera shop. 7-11's sell only recharge cards.