What to do about Singapore phone number while studying overseas?

Will you plan to use your accounts when you travel? If not, call up Telco and ask if they can suspend your line.

This means you do not use your line but you can still keep the number.

In case you need your accounts to have 2FA, there are a lot of tokens. But if your phone or token run into problems, makes sure there is someone in Singapore to help you.

Otherwise, consider switching to a super cheap Telco plan