Since the advent of the telephone, a distinction has been made  between "inside sales" and "outside sales" although it is generally agreed that those terms have no hard-and-fast definition.  In the United States, the Fair Labor Standards Act defines outside sales representatives as "employees [who] sell their employer's products, services, or facilities to customers away from their employer's place(s) of business, in general, either at the customer's place of business or by selling door-to-door at the customer's home" while defining those who work "from the employer's location" as inside sales.  Inside sales generally involves attempting to close business primarily over the phone via telemarketing , while outside sales (or "field" sales) will usually involve initial phone work to book sales calls at the potential buyer's location to attempt to close the deal in person. Some companies have an inside sales department that works with outside representatives and book their appointments for them. Inside sales sometimes refers to upselling to existing customers.