How to solve the problem of telecom going to court for prosecution?

You are the other party who signed the agreement with Telecom, and you have the obligation to repay the arrears. As for your friend, you can only choose to save it afterwards.

Telecom can also sue for less than 400 yuan, but whether it will sue depends on how telecom does it. Even if you don't sue, your arrears will be recorded in your personal credit report. It will have a bad influence on your later life. So the amount is not much, it is better to find a way to pay off the arrears first.