In terms of urban communication, Orators were extremely important and they used a standardized system of hand gestures that helped convey their message (as they lacked loud speakers, obviously)

Between cities, most of the communication was basically a courier system of messages by an order known as Cursus Publicus (literally 'public way'). Note: This was largely dismantled by Justinian. I am not aware of what supplanted, if anything. The courier system's routes are rather famous in a relic called 'the Peutinger Map' and this is the only known surviving record of their routes.