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What is a SIM card and how does it work? 

A SIM card is a small, removable card that connects your phone to a cellular network. It stores key information like your phone number and network identity. When you switch, you're provided with a new SIM card to connect your phone to the network.

 

Physical SIM cards come in a few sizes:

  • Standard SIM – The original, larger format, now largely obsolete.
  • Micro SIM – A smaller version used in older smartphones.
  • Nano SIM – The smallest format, used in most modern smartphones today.

When you sign up for a mobile plan, your carrier provides you with a physical SIM card that you insert into a tray on the side of your phone. Once inserted, your device is authenticated on the network and ready to make calls, send texts, and use mobile data.

Physical SIM cards are widely compatible, easy to transfer between devices, and supported by virtually every carrier and phone on the market.

 

What is the difference between a physical SIM card and an eSIM?

While a physical SIM is a tangible chip you can hold and insert, an eSIM (embedded SIM) is a small chip built directly into your phone's hardware — you can't remove it or swap it out.

Here's how they compare:

Feature Physical SIM eSIM
Form Removable chip Built into the device
Setup Insert into SIM tray Activate digitally via QR code or app
Portability Easy to move between phones Requires carrier support to transfer
Compatibility Works with virtually all phones Requires a compatible device
Replacement Order a SIM from your account Order an eSIM from your account

Both options connect you to the network and offer the same call, text, and data capabilities. The main difference comes down to convenience and flexibility. Physical SIMs are ideal if you frequently switch phones, travel internationally with local SIM cards, or prefer a hands-on setup process. eSIMs are great for newer devices that support them and for users who want to manage their plan digitally without handling a physical card.

 
How to buy a physical SIM card from RedPocket Mobile

Getting a physical SIM card from RedPocket Mobile is simple. RedPocket offers affordable prepaid plans on all 3 major U.S. networks, so you can choose the network with the best coverage in your area.

Here's how to get started:

  1. Visit redpocket.com/plans — Choose a monthly prepaid plan that fits your needs and budget. RedPocket offers competitive rates with no long-term contracts.
  2. Select Bring My Phone - RedPocket works with almost any 4G and 5G compatible, unlocked phone. 
  3. Select Get a SIM card Shipped — RedPocket offers SIM card kits that include all three SIM sizes (standard, micro, and nano) in one card, so it fits any phone. 
  4. Check out and wait for delivery — Your SIM card will be shipped to you. Register for an online account to track your delivery. 
  5. Activate your SIM — Once your SIM arrives, activate it online at redpocket.com/activate by entering your SIM card number and following the on-screen instructions.

Once activated, simply insert the SIM into your phone and you're ready to go.

 
Can I switch from an eSIM to a physical SIM?

Yes, switching from an eSIM to a physical SIM is entirely possible. Log in to your online account and navigate to the Line Summary. Select Replace SIM or eSIM. Learn more. 

Quick Note:

Keep in mind that some newer phones, particularly certain iPhone models in the U.S., are sold as eSIM-only and do not have a physical SIM tray. In those cases, switching to a physical SIM would require a different device.

If your phone supports both eSIM and a physical SIM slot, the switch is typically straightforward and can be completed in a matter of minutes.