In order to use 1:Many Records, like Communications, on Checklists, you must setup a separate Checklist Section.
If the Table isn't shown in the list of Tables you have to go to the "Advanced Table Properties" for that Table and set "Can be used on Checklists" to "Yes".
Add the first Checklist Item to the new Section as you would any other.
To ensure the Checklist Section is specific to the 1:Many table, you must go to the Checklist Section Configuration, and check that the "Section Table" is set to the Checklist Sections for the 1:Many table.
Multi record tables cannot be added manually, so they must be automatically entered through the "Automatically Enter Section" options on the Checklist Section Configuration or through an Auto Actions that is triggered by a Field on that 1:Many record. Checklist Sections for 1:Many tables should only contain Fields for that 1:Many table."