Report for user and assigned contacts (ACL)
I can't answer directly, but I can make an alternate suggestion for your structure. Instead of using ACL on Groups, you could use our extension which builds ACLs off a Relationship.
This would require a Relationship between your "user" and the contacts they need to call, but it would mean that you can then use this to deliver Reports or Drupal Views to see who is connected to whom, and the status of their calls etc.
If it is of interest you can find it here https://civicrm.org/extensions/relationship-permissions-acls