If you are doing business in your own name and you are paid more than $600 in a year by a client who is also in business, you have to give that client your tax ID number on form W-9 and they have to issue you a 1099-MISC. Private individuals you work with do not have to issue a 1099 and you don't need to give them your tax number.
If you don't want to give out your SSN, you can get an EIN from the IRS. It's online and only takes a few minutes. Google IRS + EIN.
