SIM farm

Hardware holding hundreds of SIM cards to send or receive SMS in bulk; a major source of supply and abuse in the SMS market.

A SIM farm (or SIM bank) is a rack of modems loaded with SIM cards, controlled by software. Legitimate uses include supplying receive-only numbers to verification platforms; illegitimate uses include bulk spam sending and fraud, which is why regulators in several countries restrict them.

Where a provider sources numbers (carrier ranges, partner SIMs, farms) shapes both number quality and legal exposure. This is also why "how are your numbers sourced" is a fair question to ask any provider.