[New] All About SIM Cards – Swapping, Resizing, Dual SIM & eSIM

Every modern mobile device has something known as a SIM card inside of it. Without a valid SIM card your phone, tablet, or hotspot will be essentially invisible to a cellular network.

But - just what is a SIM card?

SIM is short for Subscriber Identity Module - and it is the tiny bit of circuitry that identifies your account to your carrier's network.

You can think of the SIM card as containing your phone number - because essentially it does. Moving a SIM to another compatible device moves your service and your number to that new device.

But while SIM cards are simple in concept, there are still some important things to be aware of before you set off to move your service around.

For one - not all SIM cards are removable, and not all SIM cards are physically the same size. And just because you CAN move a SIM doesn't mean that it will always work as expected in your new device.

And some devices even support more than one SIM installed at a time - potentially allowing you to carry around multiple phone numbers (and data plans) in your pocket at once.

Included In This Guide:

Enjoy This Free Preview
of Our Guides

We are honored to be able to present the basic sections of this guide as a free preview to you - without 3rd party advertising, sponsorships or relying on selling you gear or plans.

In thanks for funding this resource center, MIAs (Mobile Internet Aficionados - our premium members) also get access to all of the in-depth content in this guide.

If you're a member, please log in above for full access to this guide and ability to comment.


Learn More About Membership


Introduction to SIM cards

A SIM card is usually a small piece of plastic with an embedded chip integrated into it.

This chip contains a unique serial number known as an ICCID (Integrated Circuit Card Identifier) that is cryptographically secured so that each SIM card is essentially impossible to copy.


The three common SIM card sizes.

This makes it incredibly difficult for anyone short of the NSA to impersonate you on the cell network, or to listen in on your calls or messages without the cooperation of the cellular carrier.

A cellphone without a SIM card is anonymous to the network, and it will be ignored for everything other than 911 calls and emergency alerts.

Get a free PDF copy of our ebook when you join our e-mail newsletter!

Since your identity is tied to the SIM card and not to the phone (or tablet, or hotspot) - it is theoretically possible to move your SIM card to another device to transfer your service.

This can be extremely handy – you can often take a SIM from a Mobile Hotspot and put it into a tablet, for example.

Or… you can keep an old beater or more rugged phone around for when you are heading out into rough conditions – such as a backcountry hike or kayaking. Before you head out, just pop your SIM into the adventure device and you can still keep online and get phone calls, without putting your flagship expensive smartphone at risk.

Or… when you are traveling internationally, rather than paying expensive international roaming fees, you can instead get a SIM (and a local phone number) from a local cellular company, and then get online much, much cheaper while still using your existing phone.

And if you ever break your phone - you can usually just move your SIM to a borrowed spare until you get a chance to get your primary device fixed.

The convenience and flexibility that comes from SIM cards is undeniable.

Finding Your SIM

This Netgear Fuse hotspot has a removable battery and Micro-SIM (3FF) hidden under the back plastic cover.

The first step towards taking advantage of your SIM card is finding it - and this can sometimes be difficult.

The SIM is often found lurking underneath the battery of many phones or mobile hotspot devices, and it can usually be carefully slid out of its little slot with a fingernail.

For devices that lack removable batteries, the SIM is usually in a tiny ejectable tray that can be removed by pushing a pin carefully into a pinhole - often found on the top or the side of a phone.

Or there might be a SIM slot, potentially hidden behind a cap. If the SIM is in a slot, it is usually spring-loaded. Pushing the SIM in with a fingernail will trigger the spring and eject it outward.

On other devices the SIM might be more hidden - and you may need to dig deep into the manual to find where it is lurking.

And though there is always a SIM of some sort to be found on every LTE device, in some cases (especially on things such as embedded devices like smart cars) the SIM might actually NOT be removable without voiding a warranty to literally crack open the modem module.

And even then - it might actually be soldered in place!

But fortunately - on most phones, hotspots, tablets, and cellular routers the SIM card is usually not that hard to get at.

TIP: When you remove a SIM card, pay attention to how it is oriented. It will only work (and fit) one way, and while this is often obviously indicated being certain of the correct orientation helps you avoid the mistake of accidentally wedging a SIM card in upside down or backwards.

SIM Card Sizes

Many carriers now issue "All-In-One" or universal SIM cards - just pop out the size your device needs.

SIMs have been getting smaller over the years – the original full-size SIM from the early 1990's was the size of a credit card!

But the ones you are most likely to see today are:

  • Mini-SIM (aka 2FF)
    (now often called "standard" or "regular" size)
  • Micro-SIM (aka 3FF)
  • Nano-SIM (aka 4FF)

Fortunately - even though SIM cards have been shrinking, electrically they have remained compatible. So it is (usually) possible to alter the size of a SIM card to deal with size mismatch issues.

And many carriers are now issuing universal SIM cards that can easily be punched out to fit into any device.

TIP: Though SIM cards are electrically compatible, some older SIM cards might not support features built into newer phones like Voice-Over-LTE (VoLTE) or using contactless payments to use your phone as a credit card while checking out. If you run into an oddball issue like this, your carrier should be able to replace your old SIM with a newer one.

Modifying SIM Sizes

The carriers actually make it pretty easy to obtain a SIM card of the proper size for your device. All the carrier needs to do is provision your plan to a new SIM card. This can often even be done over the phone if you have an unused carrier SIM card in your possession.

But if you have a grandfathered in plan, are SIM swapping to devices that may not be officially supported by your plan, or are frequently swapping between devices that take different sizes - sometimes you might not want to involve your carrier.

Because SIM cards are all electrically identical – it is actually possible to carefully cut down a Mini-SIM or Micro-SIM to put it into a device that has a Nano-SIM slot.

And you can use a small plastic cradle to put a smaller SIM into a Mini or Micro slot.

TIP: For a good list of what SIM sizes are used by many popular phones, look here.

The QQ-Tech SIM Cutter converts a Mini or Micro SIM into a Nano SIM.

The QQ-Tech SIM Cutter converts a Mini or Micro SIM into a Nano SIM.

Some people have been known to modify SIM cards with razor blades or scissors, but for less than $10 on Amazon you can buy a SIM cutter tool to make the process easier

Cutting a SIM can be scary the first time - especially if you have never seen it done.

To help demonstrate how SIM cards can be cut down and sized-up, we created this video guide:

Nano-SIM Caution

Nano-SIM cards are slightly thinner than the two other sizes. This usually is not an issue, but some devices have VERY tight Nano-SIM slots and you can end up with a cut-down SIM wedged inside and trapped.

Particular when swapping a cut down SIM card into a 6620L JetPack - you do need to lightly sand down the NON-electronic side of the card for it to fit. For more information on swapping into a 6620 (including a quick demo video), and what to do if you get your SIM card stuck: Opening up a Jetpack® 6620L to Remove a Stuck SIM card

On the other hand - starting with a NanoSIM and using adapter trays to size up is usually not a problem at all. If you have the option - start with a Nano!

Additional Member Only Content

If you're an MIA member, please log in to see the rest of this guide - which contains additional information on:

  • SIM Swapping - Moving SIM Cards Between Devices
  • Obtaining SIM Cards
  • Dual SIM & eSIM

Want full access to the rest of this guide?

Ready for More?

We offer a ton more content here at the Mobile Internet Resource Center.  Here's some places to check out next:

Have questions?

Join our free Internet for RVers & Cruisers Facebook Group.  We cross post news articles and information there, and our staff can field basic questions during 'business hours'. It is with gratitude to our premium members that we're able to offer this free service - and for that, they also have access our private Q&A areas for more in-depth guidance.

Stay in the Know :

We're constantly tracking the industry and analyzing new developments for mobile travelers. Check out our News Center for the latest things we're tracking.

If you'd like to receive updates, we offer several ways:

Members, Please Log In to Comment on this Article.