Do you contract out to others or plan to under a 1099?  You may be required to request a W9 for the work.  When you do accept the W9's you will need a method to verify the TIN/Name combination is valid.

You can do so online or on the phone.  Here is the IRS page on handling the verification:

http://www.irs.gov/govt/tribes/article/0,,id=131207,00.html

If for some reason you cannot find it, try searching for "tin matching" on their site.