I don't have any experience, but this site might help. Good luck! http://www.backyardchickens.com/t/906916/no-crow-rooster-collar
Mine decided to crow at 4am one morning. I love hearing it MOST of the time, but at 4am it kind of sucks. BUT, I knew what I was getting myself into (mostly anyways, I've learned things along the way, the crowing I expected though) when I ended up deciding to keep my boy (he was suppose to be a she).
I weighed out the pros and cons of keeping my guy around, and I've been pleased overall. He's a GREAT protector of the flock, and he's pretty laid back overall. I plan to try to hatch some eggs in spring so that's another reason I kept him. He's already helped to save the flock from a few intruder attempts (hawk, a neighbor's dog who dug under my fence, and a neighbor cat). He alerted me to the issue and I was able to get right out there or the end result probably wouldn't have been good at all.
Is there a particular reason you're keeping him? To protect the flock? Fertilize eggs for hatching? If you're keeping him around to protect the flock do you really want to stifle his alert calls and crows?