dual card slots

Some mobile phones support use of two SIM cards, described as dual SIM operation. When a second SIM card is installed, the phone may allow users to switch between two separate mobile network services manually, have hardware support for keeping both connections in a "standby" state for automatic switching, or have two transceivers to maintain both network connections at once.
Dual SIM phones are mainstream in many countries where phones are normally sold unlocked. Dual SIMs are popular for separating personal and business calls, in locations where lower prices apply to calls between clients of the same provider, where a single network may lack comprehensive coverage, and for travel across national and regional borders. In countries where dual SIM phones are the norm, people who require only one SIM leave the second SIM slot empty. Dual SIM phones usually have two unique IMEI numbers, one for each SIM slot.
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 support four SIMs, such as the Cherry Mobile Quad Q70.

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