Their customer service answered my email the same day. Here is their answer:
[quote]Many thanks for your inquiry.
There are 2 methods to change your messages from Chinese to English language.
Pls dial 777 from your mobile phone→ listen to your messages →
main menu (主要選項) → press 4: fax, another options menu (傳真及其他選項) →press 1:language options menu (語言選擇) →press 4 :English(英文)
Pls kindly provide your personal information (such as: ARC No, Passport No, address…etc.) to our mobile service center to change the service for you.
If you still have any questions, please don’t hesitate to contact our 24- hour Customers Service Center toll free number 0800-080090. (Dial 800 from your handset). Thank you!
Customer care department
Mobile business group
And it worked!