Pronunciation: Ohr, ,uh, tund. Rhymes with more, uh, gunned.
Origin: According to the Online Etymology Dictionary, orotund comes from Latin Ore Rotundo meaning "with round mouth".
Why use it? I like the first use much more than the second; we already have words like bombastic. But no one word has all the meanings of orotund as applied to a voice.
Examples: Most of the examples I could find online were of the second meaning of the word, but it's easy to come up with good uses of the first:
His orotund voice masked the vapidity of his viewsor
While his orotund voice got him some auditions, his utter lack of acting ability doomed his career.