Is it a microphone or isn't it? Check out MuggleNet's screencaps from the Harry Potter and the Prisoner of Azkaban trailer and decide for yourself!
Also, in case you were wondering what exactly it is the choir is singing on the trailer, they are lyrics from the opening of Act IV of Shakespeare's "MacBeth."
[i]Double, double, toil and trouble
Watch the cauldron boil and bubble
By the pricking of my thumbs
Something wicked this way comes[/i]