Copyright of lyrics

So I had the idea of using a phrase of another song in one of my songs, like Katy Perry did in 'California Girls' towards the end. Another example I guess another example would be using the phrase 'Voulez-vous coucher avec moi ce soir?,' but not singing it with same melody or maybe just speaking those words. What exactly are the rules concerning this? Where could I get help if there are any particular rules?

U.S. Copyright Office's got nice F.A.Q. page, with special chapter about using other's work, and I believe answer to your question is here - http://www.copyright.gov/help/faq/faq-fairuse.html#sued.
In couple of words, it depends on Fair Use concept - if you don't take too much and don't make it central idea of your work then it's ok, but court knows better