Simple questions: What is Dual SIM and how does it work?

Have you ever wondered what’s so special about Dual SIM smartphones? What makes them useful and how does the Dual SIM technology work? Or maybe you already know that, but you still have questions like what makes Dual SIM Dual Standby different from Dual SIM Dual Active ? If you want to know what exactly the Dual SIM technology is and

answers to these questions, or if you’re simply looking for a list with some good Dual SIM smartphones, read this article. We’ll provide both answers and examples:

What does it mean for a smartphone to be Dual SIM?

A smartphone that can hold two different SIM cards is called a Dual SIM smartphone. Having two SIM cards means that a Dual SIM smartphone can use any of them to initiate or to receive phone calls.

Why are Dual SIM smartphones useful?

For some people, having a Dual SIM smartphone can be very useful. Take for instance, businessmen and women who tend to have a different phone number for their professional contacts and another number for their personal contacts. A business person can either use two different smartphones or use a Dual SIM smartphone, with both phone numbers active on it. Having one smartphone to carry around is definitely better than carrying two smartphones.

Another common situation in which you might be interested in a Dual SIM smartphone, especially if you live in an emergent market, is when you want to use one phone number for phone calls, and the other for connecting to the internet. There are many mobile operators that have good voice plans, but pricey data plans, or the other way around. On a Dual SIM smartphone, you can combine two different plans from two different operators and get a cheaper bill at the end of the month.

What types of Dual SIM modes are there?

If you decide to purchase a Dual SIM smartphone, you should know that there are several types of Dual SIM implementations and some are better than others. The most common types of Dual SIM implementations are:

  • Dual SIM Single Standby (Passive) - it is the worst implementation of the Dual SIM technology and it is usually used in affordable phones, not in smartphones. A Dual SIM Passive phone is capable of using two different SIM cards, but only one of them can be active at any time. That means that one SIM card will work, but the other will be unreachable. In order to use the second SIM card, you need to manually activate it and the first SIM will be deactivated when you do that.
  • Dual SIM Dual Active - this implementation allows you to make phone calls from any of the SIM cards inside your smartphone, and it can receive calls on either of the two SIM cards, at the same time. Dual SIM Dual Active smartphones have both their SIM cards permanently active and, when you’re having a conversation on one of them, the other still works and receives calls, messages or data. For instance, if you’re having a call on the first SIM and you’re getting another call on the second SIM, you will get notified about it. The disadvantage of Dual SIM Dual Active phones is that these devices have two radio transceivers, one for each SIM card. This means that they consume more battery than regular Single SIM smartphones and it is more expensive to implement, leading to a higher price for your smartphone.
  • Dual SIM Dual Standby - it is a hybrid between Dual SIM Standby and Dual SIM Dual Active. Dual SIM Dual Standby lets your smartphone have two active SIM cards, but they are both active only as long as you’re not using them. Hence the name of Dual Standby. As long as the SIM cards are both in Standby mode, you can make and receive calls on any of them. However, once you take a call on one SIM card, the other becomes inactive. This is not ideal but the technology is less expensive and more widespread in today’s smartphones.

To make it easier for you to understand the differences between the different kinds of Dual SIM implementations, we created this simple comparison table:

Can you use your 3G/4G data plan on both SIM cards, when using a Dual SIM smartphone?

The short answer is Yes, but it depends on the Dual SIM implementation that was chosen by the manufacturer of your smartphone. Manufacturers look at how much their smartphones cost to build and their profit margins. Building a Dual SIM smartphone with a SIM card that supports 4G data connections and the other 2G, is easy and affordable. 4G + 2G can be combined in a Dual SIM Dual Standby mode and use the same radio frequencies. However, if you want to build a Dual SIM smartphone that supports 4G connections one of its SIM cards and 3G or even 4G on the other, that would mean that the processor on the smartphone must be powerful enough to support two high speed data connections simultaneously and probably the costs would be rather high. Most Dual SIM smartphones that we have seen offer 4G + 2G data connections.

Examples of Dual SIM Dual Active smartphones

Although Dual SIM Dual Active smartphones are obviously the best, they are rare because of their high costs. The only Dual SIM Dual Active smartphone that we know of, at this time, is the ASUS ZenFone 2 ZE551ML and we wrote a detailed review of it, here.

Examples of Dual SIM Dual Standby smartphones

Because of the good balance between their cost and the features they offer, most Dual SIM smartphones available on the market are Dual SIM Dual Standby smartphones. If you want to buy such a device, here’s a list with some good options: Samsung Galaxy S7 Dual SIM , LG G5 Dual SIM , Huawei Mate 8 Dual SIM , Xiaomi Mi 5 Dual SIM , ASUS Zenfone 2 Laser ZE550KL , ASUS Zenfone Max ZC550KL , Lenovo X3 Vibe , Huawei P8 Lite , OnePlus X and Lumia 650.


Dual SIM smartphones can be very useful in certain cases and smartphone manufacturers have started to notice that people want such devices. As such, more and more Dual SIMs are produced each year. However, as you’ve seen in this guide, not all Dual SIM devices work the same, and some Dual SIM implementations are better than others. Let us know about your experience with this technology and what you think about it, in the comments below.