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A SIM box (also called a SIM bank) is device used as part of a VoIP gateway installation. It contains a number of SIM cards, which are linked to the gateway but housed and stored separately from it. A SIM box can have SIM cards of different mobile operators installed, permitting it to operate with several GSM gateways located in different places.
Contents
Usage and detection
The SIM box operator can route international calls through the VoIP connection and connect the call as local traffic, allowing the box's operator to bypass international rates and often undercut prices charged by local mobile network operators.
This business model of operation is very common around the world and is usually legal, as it simply uses the internet to piggyback calls to a local area and using a private exchange to route the call back to the mobile network. However, many companies, such as Verizon, provide strong lobbying forces to local governments to ban the use of SIM pools. Another reason is the lack of control of the users, i.e. Knowing who called who? Creating a serious privacy challenge to the users, where (local) governments want to know who made certain calls to whom and from where. One such example is the country of Ghana, where government has banned the use of SIM boxes.
Call Quality
As the normal mobile network are usually using a very outdated and low quality sound codecs (such as the G.711 used in GSM), a SIM box may provide local VoLTE quality with superior sound quality.