900 and 500 numbers are those
numbers that have been assigned to designated
carriers to provide services on a per block of
numbers basis. 900 numbers are normally those
designated for services being charged to the
subscribers calling the number.The 500 numbers are
presently designated for use in the PCS application.
The assigned carriers are assigned numbers in
accordance with the North American Number
Planning(NANP). Routing for these numbers is
controlled on a per-switch basis. Number blocks are
rerouted to specific carriers, the carriers are then
responsible for the termination of the call using the
carrier's technology.
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