COLUMBUS, Ohio (AP) _ Sprint's telephone service for the hearing impaired was interrupted for almost an entire day due to an unexpected surge of user traffic.

The problem occurred Saturday in all 21 states that Sprint provides the service, James Fisher, a spokesman for the Kansas City, Mo.-based company, said Sunday.

Sprint received 51 percent more calls systemwide than the approximately 32,000 it expected during Saturday, causing delays to some callers using the service.

The situation lasted during most of Saturday and was resolved by Sunday, said Fisher, whose office is in Washington, D.C.

Sprint did not know what caused the rash of users, he said.

``We're just baffled,'' Fisher said.

The company scheduled a meeting Monday to determine what caused the delays.

Thomas Applegate II, president of an advocacy group in Ohio called Hear Us Now, complained that the service was entirely unavailable for a time Saturday night. Fisher said the system never went down.

Many hearing-impaired people use ``text telephones,'' also known as TTY or TDD systems, to make calls. Users type messages over a screen that are read by a text telephone operator at a relay center, who acts as a kind of interpreter between the user and the hearing person on the other end of the line.

Sprint is the nation's largest provider of phone service for the hearing-impaired. It provides the service in California, Colorado, Connecticut, Indiana, Iowa, Maryland, Minnesota, Missouri, Montana, Nevada, New Hampshire, New Mexico, New York, North Dakota, Ohio, Oklahoma, Oregon, South Carolina, South Dakota, Texas, Wyoming. It also serves all U.S. government offices.