Rams' horns serve the purpose of allowing adventurers of at least level 20 to shout a message to everyone within earshot of this audible channel, assuming they have the requisite 100 gold.
One will find rams' horns scattered across Achaea. They generally can be located on mountaintops or cliffs, although there are some exceptions. Some of the more popular locations for horns include the Vashnar Mountains, the Granite Hills, the cliffs near Riparium, the Mhojave Desert, the Underworld, and the Shrine of Ascension, among other places.