Why Dual SIM Sells
Customers run two numbers for practical reasons: one for work and one for family, one for a cheaper tariff on calls and another for data, or a local number alongside one kept from another country.
In markets where operators price on network calls very differently, carrying two SIMs is simply cheaper than carrying one. That is why the feature is asked for by name.
Dual SIM Dual Standby
The common arrangement. Both SIM cards stay registered on their networks and either one can receive a call, but only one can be in a call at a time. While a call is active on the first SIM, the second is unreachable and the caller hears the network's unavailable message.
For most customers this behaviour is fine, because the situation only arises during an actual call.
Dual SIM Dual Active
Both SIMs can be active at once, so a call can arrive on the second number while the first is in use. This needs more radio hardware and is less common in the price bands most of this region buys in.
If a customer specifically needs to take a call on both numbers simultaneously, confirm the behaviour on the datasheet rather than assuming.
Hybrid Slots And Memory Cards
Some handsets share the second SIM slot with the memory card slot, so a customer can use a second SIM or extra storage, but not both. This surprises customers after purchase and generates returns.
If the handset has a hybrid slot, put it on the shelf label. It is far cheaper to explain before the sale than to argue about afterwards.
What To Confirm Before Ordering
Ask three questions on the datasheet: how many SIM slots, whether the behaviour is dual standby or dual active, and whether the second slot is shared with the memory card.
Also confirm the SIM form factor, because a customer arriving with an older SIM card and a handset that takes a smaller one has a problem the counter has to solve.
Explaining It At The Counter
Keep it to one sentence: both numbers ring, but you can only be on one call at a time. That is accurate for dual standby and it sets the expectation correctly.
Avoid promising simultaneous calls unless the datasheet says the handset supports dual active.
