How can you find the previous owner of your current telephone number?

In general, you can't. Try a google search.

contact your phone service provider

This is easy! Just go to the local library of that exchange and ask to see the historic criss-corss directories in the reference section. If the phone number is very old, you may have to go to microfilm (you remember microfilm, don't you?) The "criss-cross" directory contains a section called the "blue pages" (name may vary) which lists the telephone numbers in order, and who has that number. These books are made every year, although recently they have been placed on CD-Rom instead of print copy. Still, you should be able to find them at your good-old-public library!

You can't because they usually move away thats why they no longer have the #.