The name Guglielmo is a boy's name of Italian origin. Guglielmo and is often added to lists like International Variations of William and discussed in our forums with posts like "Love-Like-Lose List Version -boy names-".
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.