Joke Collection Website - Blessing messages - What does it mean for the caller to display SMS calling service?

What does it mean for the caller to display SMS calling service?

the other party has a bad signal. The caller showed that the short message calling service was because the other party's signal was bad, which made it impossible to get in touch, so he switched to the letter calling service. The call service needs to be opened at the operator's outlet. When the other party's signal is good after the call service is opened, a short message will be received to inform the incoming call information.