The Communications Tab on the customer page shows you a record of certificates saved against the property and a record of emails, SMS messages and letters sent regarding this property.
If you are dealing with a Tenant, it will display a log of letters, emails and SMS messages sent not only to that tenant, but also the agent regarding this tenant property.
This means that under the Agent's communications tab there is very little displayed. What would be displayed for an Agent's communication tab is Statements.
You can also Add Certificates to the property by pressing the green plus icon next to certificates.