The name Guglielmo is a boy's name of Italian origin. Guglielmo and is often added to lists like The International Variations of William and discussed in our forums with posts like "Name Your Kids with Pics and Ages #2".
From the experts:
William is a stylish classic right now, and while translating many classic names into Italian makes them instantly cooler and more attractive, this is one exception: Guglielmo presents pronunciation problems for the English speaker, suggesting the less-than-cool word "googley" followed by the even-less-cool-than-that Elmo.
While the actual pronunciation is Goo-LYEL-mo, in this case we advise that you stick with William.