I like asking around and coordinating wanted, TIs, etc. in world (and others on my server as well), so I use all my trumpets really fast. But there's no other way that you can reach between groups and the groupless players and let people know who needs what; PM's are too impractical and then someone else just jumps in a random team XD if anyone has suggestions for fixing this... like an improvement on the matching system that shows teams by TI level and by friendship level...
U know i usually speak only to another group after GNW n sometimes i use trumpets for the last TI. There are no important things to talk about ;P
Trumpets serve the most basic of functionality in many games.
Believe it or not, You will use a Trumpet. The game just inherently gives you it so it enables you to talk. And it's relatively cheap too, in case you run out. I don't have to explain why they exist.
Considering that we all have infinite inventory, It's a filler item that enables us to talk with everyone a specific time. No real issue to sell your "Speech" for less than 10coin.
Now imagine if Trumpets cost gold? That'll be something.