You noticed the view Messaging under Activities work center and you need to understand this functionality.
SAP CLOUD FOR CUSTOMER 1711 / 03
Reproducing the Issue
Go to the Activities work center.
Go to the Messaging view.
This type of activity records all the SMS interactions made on tickets.
If you wish to use the SMS functionality, you should first enable the SMS channel.
Check Configuring SMS Channels section from SAP Hybris Cloud for Customer Admin Guide for help.
Messaging; Activity; work center; view; SMS; , KBA , LOD-CRM-ACT , Activities , How To