Why can't Unicom send text messages when it changes its 2g card to 4g card?

First of all, check whether the mobile terminal supports it. If it is a 2G terminal, it is impossible to use a 4G card. If there is nothing wrong with the terminal, we need to check whether it can't be sent to everyone or individuals. If it is everyone, it is recommended to check the number settings of the SMS center (SMS center numbers may be different in different regions, so iPhone needs to call to delete the SMS center number first, and then call to add it again. It is recommended to contact customer service). If you can't send it to someone, it's the other person's fault.