Why Unicom can't make a phone call but has a short message prompt?

According to the information provided, you can open the "Call Manager" and "Boot Reminder", and there is also a service called "Phone Bill". After handling the business, when the mobile phone is turned off, there is no power or signal, the incoming call will be transferred to the incoming call reminding voice platform, and a short message will be sent to remind the missed call. Due to the different policies of different cities, the name and tariff of the call reminder service are also different. For details, it is suggested to contact the Unicom customer service to which the number belongs.