If you’ve browsed any smartphone’s tech specs in the last few years you’re likely to see that many phones now support “dual-SIMs.”

Some Android phones have offered dual-SIM support for years, while iPhones have only gotten the feature more recently. Here’s what iPhones support dual-SIMs and what you need to know about the technology.

What Are Dual-SIM Phones?

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Dual-SIMs sound complex, but they are actually quite simple to explain. You know that tiny plastic card you slot into your iPhone? The tiny card with a chip on it? That’s a SIM card and that chip on it contains your phone number. By inserting that chip into your smartphone, that’s how mobile providers know which device to route calls and texts to when they call your number.

A dual-SIM phone, then, is simply a phone that has two slots, in which two different SIM cards can be inserted at the same time. This gives your single phone two different phone numbers.

What Would You Use A Dual-SIM Phone For?

Why would I want two different phone numbers? That’s the question many people ask when they inquire about what a dual-SIM is. And the truthful answer is: most people don’t want–or need–two different phone numbers.

However, two phone numbers linked to one phone, and thus dual-SIM phones, are incredibly useful to two specific types of people.

The first is business people. A dual-SIM phone allows them to have one phone number for personal use and one phone number for business use–all linked to the same phone. The personal number you give to your friends and family, and the business number you give to your clients and coworkers.

That second group of people that really benefit from dual-SIM phones are international travelers or people who spend a lot of time in two or more countries. A dual-SIM phone means you could keep a SIM for your mobile plan in, for example, America, and also keep a SIM for your mobile plan in, for example, Japan. This means that when you land in either country, you can quickly just switch to the local mobile carrier you use there. And if you want, you can keep the second SIM active, too, so any calls that go to your US number will still be able to be received in Japan.

Dual-SIMs can save you a lot in data charges too. When you land in the country with your second SIM, switch to it to join your local data plan there and you won’t get massive roaming charges from your carrier back home.

Are Dual-SIM Phones More Expensive?

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Dual-SIM phones aren’t more expensive, but there is an increased cost associated with maintaining two mobile carrier plans. After all, if you have a US phone number with one SIM, you’ll have a monthly bill with a US carrier. And if you have a Japanese phone number with the second SIM, you’ll have an additional mobile plan with that Japanese carrier.

What Is An e-SIM And How Does It Relate To Dual-SIM?

While many Android phones that are dual-SIM have two physical SIM slots, Apple’s approach to dual SIM is a bit cooler. That’s because iPhones that are dual-SIM have one physical SIM slot and one fixed e-SIM. An e-SIM is an electronic SIM.

Apple’s approach is cool, especially for international travelers. That’s because you can use the physical SIM slot for your mobile plan at home, but when you land in a foreign country, you don’t need to go out and buy another SIM card if you want a data plan while traveling. You can just text the local carrier or sign up for a data plan via their app. The carriers will then link your temporary plan to your e-SIM in the iPhone–no physical SIM needed!

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What iPhones Have Dual-SIMs?

All iPhones introduced in 2018 and later have dual-SIM (via e-SIM) support. These include:

• iPhone XS
• iPhone XS Max
• iPhone XR
• iPhone 11
• iPhone 11 Pro
• iPhone 11 Pro Max
• iPhone 12 Mini
• iPhone 12
• iPhone 12 Pro
• iPhone 12 Pro Max
• iPhone SE (2020)