900 number

Etymology
In the original North American Numbering Plan, phone numbers beginning with an area code of "800" were reserved for so called toll-free numbers, where the party receiving the call pays the charges. The telephone companies later developed a corresponding set of numbers beginning with the area code "900" which would permit the owner of the number to receive additional fees from the caller.

Noun

 * 1)  A telephone number for which an extra charge is assessed, part of which is returned to the owner of the number.