Looking through my Covenant Enchanted Items thread (I seem to be pointing to that thread a lot lately) will show several items that can be used for long range communication. One of those items is the Slates of Communication which is an even more simplified version.
You activate it and how you move than handle is mirrored on the other, allowing you to write and erase messages. They can be made as an enchanted item and AC item or two enchanted items. The former takes more space but avoids any chance of interference while the later is more compact though can have issues if both are activated at once.
Another type is several ring and sphere pairs (AC to each other) which allow communication between them, actually based off a published item. I just realized I slightly messed up the text in the thread, though it is corrected here [touching the AC rather than being an AC to a person].
The Map of Hermes will show the location of the ring if the sphere is slotted into it. It can also cause a small bell chime to sound from the ring, which lets that person know to activate its power so that communication can take place.
There are a couple of others in the thread, such as ones that cause remote alarms to ring and one that allows remote text to be read. Variations of the former are used as a "door bell" for those who wish to enter our Regio, an alert system to get someone of approrpate rank to meet visitors, and an alarm if some form of attack happens. The later is used to remotely read journals issued to traveling grogs as well as text held by rivals (not Magi).
The text we have AC to include ships logs for all of our trade ships, varies logs for our trading company, and journals given to varies agents (spies and scouts mostly). There are also AC collected subtly for text held by varies mundanes such as the logs of rival trade companies and port masters. And normally a few blank journals with AC that are ready to issue.