Character mistake: When Will finds April's lost copy of Jane Eyre, the book shop clerk reads the inscription written by April's dad and says it's a quote from the book. It's actually a quote from Bronte's poem Evening Solace.
Factual error: The flashback where it shows him flying to New York shews the Twin Towers, but also 432 Park Ave which was built after the world trade center was destroyed. (00:11:42)
Chosen answer: The closest thing to them available in reality appears to be these: http://www.sennheiser.com/sennheiser/icm_eng.nsf/root/press_releases__07.01.2008.