A 1-900 telephone number, in the North American Numbering Plan, usually has the form 1-900-###-####. A call to one of these numbers can result in a high per-minute or per-call charge. For example, a "psychic hotline" type of 1-900 number may charge $2.99 for the first minute and 99 cents for each additional minute.
Some uses of 1-900 numbers:
Video game tips
Horoscopes/psychics
Dating/party lines
Erotic one-on-one chats
Voting (e.g. for TV shows)
Contests
Phone lines can be configured to prevent the dialing of a 1-900 number, but said configuration is not done by default - the customer has to call the phone company.
The issuing of these numbers to service providers is typically regulated by a national body, such as ICSTIS (the Independent Committee for the Supervision of Standards of Telephone Information Services) in the United Kingdom, to ensure certain community standards are adhered to both in terms of content and price.
These telephone numbers are usually allocated from a national telephone numbering plan in such a way that they are easily distinguished from other numbers.
A 1-900 telephone number, in the North American Numbering Plan, usually has the form 1-900-###-####, as is often called a 900number or a 1-900 number ("one-nine-hundred").