From my personal experience I think some numbers do get reused. When I first got my Google Voice number I kept getting a bunch of calls asking for some other person, so I guess Google just reused someone else's old number.
Numbers do get reused. I live in Paris and last year a friend freshly arrived from my hometown in Portugal was attributed the cellphone number (major French operator) from a german acquaintance of mine that had moved out of Paris a year before. She still gets text messages in German all the time.
