A Guide to Dual SIM

A dual SIM smartphone can support two SIM cards. Whether it’s two physical SIM card slots, or eSIM technology, here’s everything you need to know about dual SIM.

What is dual SIM?

Mobile phones require a SIM card to connect to a mobile network. Dual SIM is when a mobile phone has the option to use two SIM cards on a single device.

There are two ways a mobile phone can support dual SIMs:

  1. Dual physical SIMs - a phone that has two physical SIM card slots
  2. eSIM - a phone that has one physical SIM card slot, and one eSIM built into the device

A mobile phone with dual SIM cards allows the user to standby on two separate mobile networks. This means you’re able to make and receive phone calls and SMS from two different phone numbers, on a single mobile device. You can also use mobile data from the two different networks, however you may only use the internet on one network at a time.

What is the difference between dual SIM and eSIM technology?

An eSIM is an electronic or embedded SIM card that’s built directly into a mobile phone. A mobile phone with eSIM capabilities also has one physical SIM card slot. This means you’re able to use two different mobile networks; one using the physical SIM slot and one using the eSIM.

This is different from Dual physical SIMs, which uses two physical card slots. To learn more about eSIM and the eligibility for Optus Customers read eSIM: What you need to know. Currently eSIM is available to new, recontracting, and existing Postpaid Mobile customers with an iPhone XS, XS Max and XR, running iOS 12.2 or later.

What is the advantage of a dual SIM phone?

Having the ability to use two different mobile networks on the same mobile device is useful in several situations.

1. One phone for work and personal use

The benefit of using a dual SIM mobile phone is that you’re able to make and receive calls and SMS from both your personal and work phone, all on the one device, rather than having to carry around two separate mobile phones.

2. International travel

Dual SIM means you can take advantage of local plans while travelling overseas.

You can insert a local SIM into one of the SIM card slots to use for making calls and using data. At the same time, you can keep your Australian SIM in the other card slot, so that you remain available for incoming calls and SMS to your personal number.

3. Getting the best deal

Dual SIM also allows you to take advantage of the best mobile plans to suit your needs. Because you can only use one of the SIMs for mobile data at a time, you can pick a plan with an appropriate data allowance for this SIM. You can then use the other SIM card slot for calls and text, without having to worry about the amount of data allowance on that plan.

Why wouldn't you want a dual SIM phone?

While Dual SIM is a great benefit for business-people and travellers, there are some downsides.

In some phone models, the second SIM card slot takes the place of the microSD slot. In these circumstances you cannot use a microSD card to extend your phone’s storage space. If you want to avoid this potential problem, look for a Dual SIM phones with higher built-in storage space.

How can I use mobile data in a dual SIM phone?

While you can make and receive calls and SMS from either SIM card in Dual SIM phones, you can only have one active data connection to the internet. In the Settings section of your phone you are required to set your preferred SIM for connecting to the internet.

How to set preferred SIM for data usage on DUal SIM Android

How to set preferred SIM for data usage on Dual SIM Android mobile


How do I know if my phone is dual SIM?

There are a number of ways you can check if your phone is dual SIM:

  1. Open the SIM card settings on your device and see if there are two options
  2. Check the phone package for two IMEI numbers
  3. Search for your phone in the Device Guides.

Can I use one SIM card in a dual SIM phone?

Yes. You can use just one single SIM card in a dual SIM phone. The second SIM card slot simply gives you the option to use a second SIM card if you would like.

What types of Dual SIM modes are there?

There are different types of Dual SIM modes:

1. Dual SIM Dual Active

Under Dual SIM Dual Active, both SIM cards are active at the same time. This allows you to make and receive phone calls from either SIM, at the same time. Even if you are on a phone call on one of the SIMs, you can receive a call coming in on the second SIM.

A phone can only be in Dual SIM Dual Active mode if it supports Dual 4G and both the SIMs are working on VoLTE. If one of the SIMs drops to 3G due to network coverage, the phone will switch to Dual SIM Dual Standby mode.

What is dual VoLTE?

Dual VoLTE is a subset feature, allowing you to make HD calls from either SIM. If you have two SIM cards that both facilitate VoLTE, you can choose either SIM before making a call.

2. Dual SIM Dual Standby

When a phone is in Dual SIM Dual Standby mode, both SIM cards are active and can make and receive calls while they are both in standby mode (i.e. neither are in use).

Once one SIM card is in use (i.e. you take a phone call), the other SIM card becomes inactive for the duration that the first SIM card is in use.

This is because the two SIM cards in Dual Standby phones use the same receiver. Once a call on one SIM card is engaged, it will use the receiver exclusively and the other SIM will lose mobile connection.

To avoid missing a calls from one SIM while the other is engaged, you can set up call forward.

How to set up call forwarding on a dual SIM phone?

When a phone is in Dual SIM Dual Standby mode, and one SIM is engaged in a call, you will miss any incoming calls from the other SIM that occur during the time that that first SIM is engaged.

To overcome this issue, you can set up call forwarding between the two SIMs. See this page for instructions on how to set up call diversion on mobile phones.

How do I activate dual SIM?

If your phone is single SIM it cannot be converted into a dual SIM phone.

If your phone is Dual SIM, you can activate it by inserting two SIM cards – one in the first SIM card slot, and a second SIM card in the second SIM card slot. The activation settings for Dual SIM can be accessed in your phone’s settings.

How do I turn off one SIM on a dual SIM phone?

You can turn off one SIM card in the settings section of your phone. The settings options may vary between devices. For dual SIM settings specific to your device, search your device in our Device Guides.

If you do not wish to use a second SIM card, you could also remove the second SIM from the SIM card slot.

How to turn off one SIM in Dual SIM phone in Settings on Huawei P30 Pro

How to turn off one SIM in Dual SIM Phone Settings on Huawei P30 phone


Optus devices supporting Dual physical SIMs

What about Dual SIM iPhones?

Currently, Apple doesn’t produce an iPhone with two physical SIM card slots. However, the iPhone XS, iPhone XS Max and iPhone XR support eSIM, which allows you to connect to two mobile networks using the single physical SIM card slot, plus an eSIM. You can read more about eSIM and iPhone here.

If you still have a question about Dual SIM, ask our Yes Crowd community.