In copyright law there is a doctrine called "fair use" that is an exception to copyright law--i.e., you don't have to get permission to use the work if it is done under "fair use". The key here is that you are using it (I assume) for non-commerical purposes and, I assume, you will use a short part of the piece of music. Moreover, no one is going to be able to use your vm greeting as a substitute for the real think so it won't affect sales.
I don't think you have a problem.