HOW TO BUY PREPAID SIM CARD
You can buy prepaid sim card at the airport , in 7-11 convenience stores and telephone shops in Taipei city.
You need to prepare the passport and the second personal document e.g.. driver lience, ID card with you as you purchase it, the shop needs that information to confirm your personal information ,then you can purchase it.
Please note that you need to make sure that your smart phone are not locked by your phone company. If locked, then you can not use Taiwan prepaid sim card, such like the phone from USA .