Customer: An individual or business that purchases the goods or services produced by a business. The customer is the end goal of businesses, since it is the customer who pays for supply and creates demand.
Internal customers are employees, suppliers, dispatchers. Basicly anyone who works or sells for the organisation
External customers are people who walk in off the street or ring in, just consumers with no connection to the organization directly that want to purchase a product/service
In my opinion they are both equally important.
http://wiki.answers.com/Q/What_is_the_difference_between_internal_and_external_customers
http://www.investopedia.com/terms/c/customer.asp
