Corporations or LLCs, employers, and, in some states, those businesses that are also getting a Seller's Permit are required to obtain a Federal Tax Id (FEIN) and a Business License. 

You can use a federal tax id number as your business id number. 

Otherwise, you will need to use your social security number over the phone or the internet all the time for orders or other business identification reasons. 

And your don't want your social security out there if you want to protect your identity.