The documentation for mobile connect in journey builder has the following two points:
Ensure the MobileConnect Demographic data extension contains the contact data used to personalize any messages used as part of Journey Builder.
Ensure that all contacts you wish to participate in your Journey Builder activities subscribe to the appropriate short or long code and keyword.
How can the contacts coming in through automation studio into journey builder be subscribed to the short code if the data coming is coming on the fly(Automation studio listening to ftp server for import and then updating a data extension)
Also how is the personalization done using the MobileConnect Demographic DE.Is it something that is done while creating the message in mobile connect that is later configured in the journey builder.