Yes, and actually the partials (Brass player jargon for which notes you can move to with your lips, without adjusting anything else) of the trumpet/bugle was based of of a rams horn.)Video

Here's the thing, brass instruments and ram horns are not particularly different when it comes to acoustics.

When playing that kind of instrument, the player's lips work as an oscillator (thing that produces the "note") and the air inside (and a little bit outside) the instrument becomes a resonator (thing that makes the note sound louder). A long instrument can play lower notes, a small instrument can play higher notes. How much the instrument widens from mouthpiece to bell also has an effect, but it is not particularly relevant if the instrument is completely straight, twisted or something in between.

A hose can be played as a trumpet. You can also get some kind of brass sound from a conch shell.

Some nice people from the University of New South Wales put together a very nice website explaining the basic acoustics of several instruments.

Horns and conches were used in antiquity (some times mentioned as used by common people, rustics, also by some foreign people not civilized enough to have proper war trumpets). They emptied horns and conches to get an air column (an animal horn is prepared for blowing by first removing the bony core with hot water or simply leaving the horn exposed to the air and flies).

The horns of rams and oxen were used to make instruments in the so called middle ages.