Dual SIM

A dual SIM mobile phone is one that holds two SIM cards. Dual SIMs are popular in locations where lower prices apply to calls between clients of the same provider; they also allow separate numbers for personal and business calls on the same handset.

Devices that use more than two SIM cards have also been developed and released, notably the LG A290 triple SIM phone, and even handsets that can run on four SIMs, such as the Cherry Mobile Quad Q70.

The first phone to include dual SIM functionality was the Benefon Twin, released by Benefon in 2000. It wasn't until the late 2000s, however, when more dual SIM phones entered the marketplace and started to attract mainstream attention, most of them coming from small Chinese firms producing phones using Mediatek systems-on-a-chip.

Such phones were initially eschewed by major manufacturers due to potential pressure from telecommunications companies, but in the early 2010s Nokia, Samsung, Sony and several others followed suit, with the Nokia C2-00, Nokia C1-00 and Nokia C2-03 and most notably the Nokia X, phones from Samsung's Duos series, and the Sony Xperia Z3 Dual, Sony Xperia C and tipo dual.

Prior to the introduction of dual SIM phones, adapters were made for phones to accommodate two SIMs, and to switch between them when required.

Dual SIM switch phones, such as the Nokia C1-00, are effectively a single SIM device as both SIMs share the same radio, and thus are only able to place or receive calls and messages on one SIM at the time. They do, however, have the added benefit of alternating between cards when necessary.

Dual standby phones, such as those running on Mediatek chipsets, allows both SIMs to be accessed through time multiplexing. When making or receiving calls, the modem locks to the active channel; the other channel would be ignored and thus unavailable during the duration of the call. Two examples of Dual-SIM Standby smartphones are the Samsung Galaxy S Duos and the Sony Xperia M2 Dual.

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