The Type Allocation Code identifies a particular model (and often revision) of wireless telephone for use on a GSM, UMTS, LTE, 5G NR, iDEN, Iridium or other IMEI-employing wireless network.
As a result, a manufacturer now simply requests an eight-digit Type Allocation Code for a new phone model from the international GSM standards body, instead of submitting a device for approval to a national review body.
The Osmocom project maintains a crowdsourced TAC database, which is CC-BY-SA v3.0 licensed and fully downloadable.
Some OEMs publish TAC data for their products: In New Zealand with the rollout of the government subsidized rural broadband initiative a way was required to prevent users inserting the rural broadband SIM cards in an unauthorized devices to get subsidized data rates.
A company wishing to resell Vodafone RBI is required to supply a device for the approval process and certification, and to supply One NZ with the TAC details of this device to embed into the SIM cards at the point of manufacture.