In telecommunication, a Wide Area Telephone Service (WATS) is a toll service offering for customer dial-type telecommunications between a given customer [user] station and stations within specified geographic rate areas employing a single access line between the customer [user] location and the serving central office. Each access line may be arranged for either outward (OUT-WATS) or inward (IN-WATS) service, or both.
In other words, with "outward WATS" the calling party may make an unlimited number of long distance calls (toll calls), for a fixed price, within pre-determined time and distance constraints. With long distance costs at historic lows, this type of arrangement has become common, and instead of "outward WATS" it is known simply as a "flat-rate plan."
With "inward WATS," subscribers are issued a toll-free telephone number, typically beginning with a designated toll-free area code such as "800", "888," "877", "866" etc., and anyone may call that number without having to pay a toll charge. The recipient pays for the calls at a flat rate or other predetermined rate. "Inward WATS" service is available with Automatic Number Identification (ANI), a form of super-Caller ID.
Note: The offering is for fixed-rate inter- and intra-LATA services measured by zones and hours.
Source: from Federal Standard 1037C and from the Code of Federal Regulations, Telecommunications Parts 0-199
