If you have a telephone number, how do you find out whose name it is
in and their address?

If you are only looking for basic information on phone numbers, (Name
listed in and Address) you can use one of several 'reverse lookup'
sites for this.
You may have trouble if you are trying to find information on a
toll-free phone number, or a cell phone number.  There also may be
some issues if the phone number in question in 'unlisted', but perhaps
this is all you need.
I personally suggest anywho.com, but a general search for "reverse
lookup" will get you more sites if this is what you need.  Here's the
link for anywho:

http://www.anywho.com/rl.html

Hope this helps,
Trea

switchboard.com is a good webiste