Wide Area Telephone Service (WATS) was a flat-rate long-distance service for customer dial-type telecommunications in the service areas of the North American Numbering Plan (NANP).

The service was between a given customer phone (also known as a "station") and stations within specified geographic rate areas, employing a single telephone line between the customer location and the serving central office. Each access line could be arranged for outward (OUT-WATS) or inward (IN-WATS) service, or both.

WATS was introduced by the Bell System in 1961 as a long-distance flat-rate plan by which a business could obtain a special line with an included number of hours ('measured time' or 'full-time') of long-distance calling to a specified area. These lines were most often connected to private branch exchanges in large businesses. WATS lines were the basis for the first direct-dial toll-free 1-800-numbers (intrastate in 1966, interstate in 1967); by 1976, WATS brought AT&T Corporation a billion dollars in annual revenue ($5.53 billion in 2024 dollars)

For outbound calls, the 1984 AT&T divestiture brought multiple competitors offering similar services using standard business telephone lines; the special WATS line was ultimately supplanted by other flat-rate offerings. The requirement that an inbound toll-free number terminate at a special WATS line or fixed-rate service was also rendered obsolete by the 1980s due to intelligent network capability and technological improvement in the 800-service. A toll-free number may now terminate at a T-carrier line, at any standard local telephone number or at one of multiple destinations based on time of day, call origin, cost or other factors.

For Outbound WATS, the United States was divided into geographical Bands 0 through 5. Band zero was intrastate calling and bands 1 through 5 (or 6) were interstate calls that were progressively further from the originating number. Historically, the higher band number carried a higher price per month or per minute. These lines could be used for outbound long-distance only; not local. In the U.S., interstate WATS lines could not be used for intrastate calls, and vice versa. With wider availability of inexpensive long distance using regular business lines, OutWATS service became obsolete late in the 20th century.

A form of toll-free telephone service in North America was the Zenith number, published in distant cities from where a company expected or desired frequent customer calls. Published as "Zenith" and a four- or five-digit number, these collect calls required operator assistance. The subscriber of the service was charged for the call.

With "inward WATS", introduced for interstate calls by the American Telephone and Telegraph Company (AT&T) in 1967, subscribers were issued a toll-free telephone number in a designated toll-free area code. Unlike a standard collect call or a call to a Zenith number, 1‑800 normally may be dialed directly with no live operator. Callers within a designated area could call without incurring a toll charge as the recipient paid for the calls at a fixed rate.

The introduction of InWATS fortuitously fell around the same time as the early centralized, automated national airline and hotel reservation systems, including Sabre (American Airlines, 1963), Holidex (Holiday Inn, 1965) and Reservatron (Sheraton, 1969). Hundreds of local reservation numbers for a major chain could be replaced with one central number, backed by a national computerized reservation system.