Is There An Internal Messaging System With Jamroom?
Yes - Jamroom features a "Private Notes" module that allows users to send private notes back and forth to their followers:
https://www.jamroom.net/the-jamroom-network/networkmarket/79/private-notes
Site Owners can also send out Newsletters to all of their users using the Newsletter module:
https://www.jamroom.net/the-jamroom-network/networkmarket/63/email-newsletters
You'll find documentation on both of these modules here:
Private Notes:
https://www.jamroom.net/the-jamroom-network/documentation/modules/286/private-notes
Newsletters:
https://www.jamroom.net/the-jamroom-network/documentation/modules/283/email-newsletters