As a cold caller I use like mentioned, the company name and state or location. Many places have a few offices. Once you find a number, its likely a customer service number answered by some call center half way across the country or world. Some cases they can get you to the right dept or an administration number, HQ number, etc. Of couse once you get to that number, its setup to block most cold callers or customer serice needed people.
Basically you have the option to enter an ext for whom you want to speak with or given another number to call for customer service. In most cases, zero does nothing, but try a few exts, then once you get someone or voice mail, press zero, that can usually get you to a front desk, etc.
Opps, did I say too much?