Thousands-Block
US (pooling rate centers); Canada phasing pooling in by exchange, 2026–2027 · also called 1K block, block
A pooled block of 1,000 consecutive numbers within an NXX (e.g. 626-470-0XXX) — under pooling, the unit numbers are allocated in.
A thousands-block is a set of 1,000 consecutive telephone numbers — the first digit of the four-digit line number identifies the block, so 626-470-0XXX is one block and 626-470-1XXX is the next. Under number pooling, blocks (not whole NXX codes) are the unit allocated to service providers, which conserves numbering resources.
A single NXX can be divided into ten blocks held by different carriers. Each block carries a status such as assigned, available (in the pool), or retained by the original carrier.
A thousands-block being "assigned" describes an allocation to a carrier, not that all 1,000 numbers are in use by subscribers. Prefix- and block-level assignment is not the same as number-level utilization.