A toll free number is designed to give a company a geographic anonymity while allowing a free to call service. Being free to call means the company subsidises the cost for their callers so there customer can call for free. Please note that some countries do not support mobile phone free surcharge, basically meaning that some countries like the UK charge callers from mobile phones to call toll free numbers.
Toll free numbers are generally in country only and are not normally viable for international calling. However there are companies like that allow you to purchase toll free numbers from anywhere in the world, allowing to route internal country toll free numbers to anywhere in the world, giving you as a company the ability to advertise where you like. For example, these USA toll guys can route to any international location, giving you the ability to be able to advertise your product or service in the USA while being based in Europe and with the explosion of the Internet this makes your services more viable Internationally.