What is a Dual SIM Phone?

The SIM card in your phone is responsible for your mobile number and network connection, and without it, your phone won’t function correctly. Most people know this, but did you know some phones can support two SIM cards?

If you think it’s about time to trade in your phone for cash and get a device, have a think about whether a dual SIM phone could be right for you.

What is a Dual SIM Phone?

As the name suggests, a Duel SIM phone has two SIM card slots in the SIM card tray, whereas a regular phone only has one. This allows you to switch between two different phone numbers, data plans or networks from one device, providing the phone itself is not locked to a network provider.

There are two main types of traditional dual SIM, and a third, embedded SIM:


DSDA stands for Dual SIM Dual Standby. When you’re using one SIM in your dual SIM phone, the other goes into standby and can’t be used. If someone tries to call your SIM 1 number whilst you are on a call on your SIM 2 number, the SIM 1 caller will hear the engaged tone.

With DSDA, only one SIM can be connected to the internet, although many have a feature called Hot Swap, which allows you to select which SIM you use for data from your settings menu. If you have a DSDA phone without the Hot Swap feature, you’ll want to put the SIM you’ll be using for the internet into slot 1 of the SIM card tray, as that’s the primary slot and the only one permitted to connect to the internet.


DSFA stand for Dual SIM Full Active. These devices allow you to receive calls from both your lines simultaneously. If you’re on a call on your SIM 1 number and someone calls you on your SIM 2 number, you’ll receive an alert and call take both calls at the same time. This type of dual SIM device comes at the expense of increased battery consumption.


It’s worth giving an honourable mention to eSIMs. These are not dual SIM phones by themselves, but they can serve a similar function. A small chip embedded into the device acts like a SIM card, except you can store more than one network on it and switch between the two, or use it in tandem with a nano-SIM, much like a dual SIM device.

Support for eSIMs is not universal across all networks and devices at this time, but they are starting to pop up more frequently in flagship models and smartwatches. So if you’re to buy refurbished phones with eSIM support, the good news is there are already models available at fantastic prices.

Who Would Use a Dual SIM Phone?

Not everyone needs a dual SIM phone, but they can be convenient, particularly if you have two phone numbers. If you have a personal phone and a work phone, having a dual SIM will save you from carrying around multiple handsets.

They can also help you keep your work and personal life separated if you’re the kind of person who uses one number for both work and play. Getting a dual SIM phone will allow you to use one handset, but you’ll be able to see which line the call is coming through, allowing you to reject if it’s outside of working hours.

Dual SIMs are also helpful for people who travel a lot, allowing you to have a local SIM for a particular country in one slot and your usual SIM in the other. This can help avoid hefty international roaming charges.

They’re also a good choice for anyone concerned about coverage or outages. If your phone network goes down, a dual SIM allows you to switch to another network and stay connected.

Who Makes Dual SIM Phones?

Dual SIM phones used to be relatively rare in the UK and were much more prevalent in other parts of the world. However, there are now a number of dual SIM phones available here, including models from major manufacturers like Samsung and Apple.

The Samsung Galaxy S21+ comes equipped with both a Nano-SIM slot and an eSIM, allowing you to change networks without swapping the SIM card out. It’s a similar situation with the iPhone 12 Pro, and if you’re looking for a top-spec dual SIM phone, you’ll be pleased to know both the Samsung Galaxy S21 Ultra and the iPhone 12 Pro Max support dual SIM functionality.

If you’re on the hunt for a dual SIM device, head over to the Mazuma Shop and start browsing our selection of refurbished phones. If you want to know what type of SIM each device supports, scroll down and select the Specification tab on the product page. If you’re on the fence about whether a refurbished device is right for you, have a read of our article on why you should choose a refurbished phone, and don’t forget, you can sell an old mobile to us too once you’ve found your next device.

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