How to send short messages when the telecom is down?

This is to prove that the number you dialed, that is, the other party's number is not being used normally now. Abnormal use cases include arrears of downtime, registration of downtime, or participation in the use of contract machines and cards alone, resulting in default downtime.

Shutdown may have the following two situations:

1, really shut down

2. Add your number to the rejection number through some calling software, which is similar to the blacklist function.

If so, send a text message. If the other party doesn't change the number, they will see the text message. If the other party does change the number, they won't accept your apology. Find an opportunity to apologize later.