SIM box

[1][2] In voice communications, typically a private exchange is used receive traffic from a local area, and the calls are routed over the internet to a SIM box in a remote region.

This business model of operation is commonly used to avoid higher tolls for non-mobile long distance calls, particularly those associated with lesser-developed countries.

SIM boxes are often used for lower rate VoIP to MNO termination purposes, including avoidance of high tolls in violation of carriers' acceptable use policies and the sending of mobile text messaging spam.

[2][3] A lot of Sim Boxes are used by scammers for sending out millions text messages purporting to be from ATO, Centrelink, Medicare, Australia Post, Commonwealth Bank, Transurban, and Linkt.

[4] As the normal mobile network are sometimes using a very outdated and low quality sound codecs (such as the GSM HR and FR codecs), a SIM box may provide local connectivity with superior sound quality.