Regulations Governing Number Portability Article 13

Mobile Operators shall provide Number Portability for their subscribers upon the date of obtaining allocated telephone numbers.
中文原文 號碼可攜服務管理辦法第13條
行動經營者應自獲核配之電話號碼開始營業之日起,提供其用戶號碼可攜服務。

English translation for reference only; the Chinese text prevails. Not legal advice.