This was a trick that I picked up while in college. We would always seem to have more empty bottles around the house then clean drinking glasses. So what would any college students do, of course we decided to make more glasses to drink from. This solved two problems at once for us.
The process of separating the top neck from the base is something that make take a few attempts. Just make sure you have a few empties to practice on first. Now remember you are working with glass and fire so safety first!