Dual SIM mobile phones are designed in nearly the same way as any other phone with the addition of a second transceiver which allows it to implement two separate Subscriber Identity Modules (SIMs). These small chips or cards slide into the backs of most mobile phones and help pick up cellular signals. They are generally programmed to pick up the signal from a particular mobile network, receiving signals from that network’s cellular towers.
Most dual SIM mobile phones maintain the use of one sole network or phone company. That is, each SIM card operates under the same wireless provider. In some instances it may be possible to use a SIM card from a second provider with the same phone, provided the additional card is the proper size and with the assumption that the mobile phone is not locked. A locked device is programmed to only pick up signals by the wireless provider that issued the phone no matter which SIM card is inserted. A card from another provider will not work in such a phone unless it is unlocked by the wireless provider.
Not all phones can accept dual SIM cards, but there are adapters available to turn almost any late model phone into a dual SIM phone. Some adapters may require both SIM cards to be cut down and fitted, while others may offer a more tailored fit. When using adapters instead of a dual SIM phone, it may not be possible to use both SIMs at the same time. Users must switch from one to the other by using an on screen menu.
Full functioning dual SIM mobile phones, by comparison, do not usually require the user to choose between one SIM or another. Both phone numbers can be used at the same time. This feature is convenient for those who wish to separate business and personal calls using two separate phone numbers, as well as those who travel frequently and want a local number for each location.
In some parts of the world the dual SIM phone has been taken a step further with phones that can hold three SIM cards. These are generally bulkier than traditional one-SIM phones. They are also not as widely used or desired as single and dual SIM mobile phones.
Drawbacks to owning a dual SIM mobile phone include a larger and more bulky appearance, as well as a shorter battery life. Dual SIM phones generally must be charged much more frequently unless they contain dual batteries: one for each SIM card. Phones that have one battery for each SIM fair much better in this respect, but are also much larger than traditional dual SIM phones. The trade off in style for longer battery life or vice versa is at the discretion of the consumer, with either option having obvious advantages and disadvantages.