To begin with 'ISP' is short for 'Internet Service Provider' and is a company like Tiscali or Aol who provide connections to the Internet. A normal ISP like AOL will pay for a vast amount of equipment, employees, phoneline support and other typical business expenses. A virtual ISP differs because they do have any such expenses, their ISP service is just a front for another. For example a new ISP called 'meganet' is created who begin an advertising drive to attract new users. They havent the funds to pay for the equipment or employees so ask AOL to provide this. It's somewhat like supermarkets like 'Tesco' who pay companies like 'Hovis' to bake their bread but package it as 'Tesco's Finest Bread'.