How to recover the information of an unlisted telephone number?

• Hi! I am running my own business. I want a favor from you all. My issue is that one of my clients hasn’t made his payment since last four months and I am having his phone number only. I have searched for his address but was not able to find it anywhere as I think it is an unlisted number. But I really want back my money. Is there any hope to recover his full information?
  Any help is appreciated.

  18 Jun 2008, 12:07 Raymond