Why you want one. If you don't know, a dual SIM card phone is just what it sounds like: a GSM handset with slots for two SIM cards. SIM cards, as I'm sure you know, are the little plastic (or one day ) cards that give your phone its number and identify you as as a subscriber to a carrier when you make a call.
https://www.cnet.com/news/why-you-want-a-dual-sim-phone/
The SIM card is used to authenticate you to your GSM carrier. This means you can remove your SIM card from your cell phone and place it into another GSM phone and use it. Conversely, if you travel overseas, you might pop in a SIM card for another carrier serving that country into your phone.
https://www.timeatlas.com/sim-cards/
All GSM phones need a SIM card to run. Some of the newer phones that use a 4G LTE network also need the card even though they are on a CDMA system. A SIM card is a tiny printed circuit board that identifies you to the phone network. Each carrier has their own SIM cards and they can vary in size based on the phone.
https://www.timeatlas.com/sim-cards/
The SIM card identifies your device on your network. When it's in a phone, it stores your phone number and sometimes your contacts and other data. The SIM card in your iPad doesn't add any phone features to your tablet; instead, it allows you to access the cellular network for data when a Wi-Fi connection isn't available.
http://smallbusiness.chron.com/sim-card-slot-used-ipad-63804.html
Pre-paid SIM cards are also available, allowing a phone that's locked to the pre-paid carrier's network or an unlocked phone to be used without a long-term contract. This type of card is useful for people who don't want to be tied to one carrier, or who want to try out a service provider before committing.
http://www.wisegeek.com/what-is-a-sim-card.htm
A Subscriber Identity Module (SIM) card is a portable memory chip used mostly in cell phones that operate on the Global System for Mobile Communications (GSM) network. These cards hold the personal information of the account holder, including his or her phone number, address book, text messages, and other data.
http://www.wisegeek.com/what-is-a-sim-card.htm
If you’re a cell phone user whose carrier uses the GSM standard such as T-Mobile, AT&T, Vodafone and others, your phone includes a tiny electronic card that offers a lot of value. The card is called a SIM (Subscriber Identity Module) card and it can maintain your preferences.
https://www.timeatlas.com/sim-cards/
A sim ( subscriber identification module ) card is a mediator between the service provider(ex:airtel) and the mobile device which authenticates the user to access the teliphonic services like calls messages and internet. Usually sim card comes with a storage capacity of 250 contacts. Views · View Upvotes.
https://www.quora.com/What-is-the-purpose-of-a-SIM-card-in-a-mobile-phone
If you use a Wi-Fi + Cellular version of the iPad, your tablet may come with a SIM card slot tucked into the side. In the United States, the only major carriers that use SIM cards are GSM-type carriers AT&T and T-Mobile. AT&T is the only GSM carrier that sells the iPad as of early 2013. If you picked up your iPad through Verizon or Sprint, you won't have to deal with the SIM card.
http://smallbusiness.chron.com/sim-card-slot-used-ipad-63804.html
When I think about the features that I need in a smartphone, I tend to be pretty practical. Sure, apps, a media player, and a good-quality Web browser are great, but what I really want is a good dual-SIM card phone. And fortunately for me, the 2013 Mobile World Congress didn't disappoint.
https://www.cnet.com/news/why-you-want-a-dual-sim-phone/
what is purpose of sim card
Subscriber identity module card is used to authenticate you to your Global System for Mobile communication carrier.