I've seen a few of these projects online lately and really wanted to have a go myself - got my opportunity this week when I picked up an old decorative bugle for £1 at the car boot.
It only took an hour or two to complete, and made for an excellent evening's tinkering.
Step 1: Horn Trimming
I had a rough idea of the shape I wanted, so set about chopping down the horn, using my all-time favourite tool a copper pipe cutter, the kind you keep tightening and rotating, like in the opening credits for Cool Hand Luke but on a smaller scale.
Step 2: Wooden Base
I happened to have handy a wooden menu holder ideally shaped to hold the horn at the right height for my phone's speaker. I drilled through and then snugly fitted the horn in place.
Step 3: Final Tweaks
With the pipe fitted through the drill-hole all that remained was to cut it to the right length, so that the phone would lie comfortably against the wood with the speaker flush with the end of the pipe. I needed to file the pipe mouth at an angle to make the fit perfect.
It looks great with or without the phone, and works a treat. Looking out for something bigger for the next one!