Your SIM card is what enables your smartphone to work on the wireless cellular network; it identifies you and your phone and contains information about your cellular provider so you can complete calls and transfer data.
Usually your SIM card works exactly as intended, but there are a few reasons it might not be working. You might not get a specific error message — your phone simply can't connect to the network — but more commonly you'll see an error that says your SIM card isn't working or isn't installed. If that's happening to you, here are the most common ways to troubleshoot your phone and get your SIM card back up and running.
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Toggle airplane mode
If you suspect there's a problem with your SIM card, it might actually be a software issue with your phone that's easily remedied with a few simple troubleshooting tricks that don't involve opening your phone and touching the SIM card at all. For example, some SIM card errors can be remedied simply by switching your phone into Airplane mode and then back again.
On most phones, including iPhone and Android, just swipe down from the top right of the screen to show the Control Center or quick settings. Tap Airplane mode to turn it on, wait a few seconds, and then tap it again to turn it off. Try to make your call again to see if this solved your problem.
Restart your phone
Another way to clear out a temporary glitch is to turn your phone off, wait about a minute and then turn it back on again. Here is how to restart an iPhone. If you have an Android device, you can generally swipe down from the top of the screen and tap the Power icon.
Remove and reinstall the SIM card
If you still see an error message or otherwise can't complete a call, you might need to reseat your SIM card. To do that, find the SIM card removal tool that came with your phone — you can also use a pin or very thin paperclip and insert into the hole near the SIM card try until the tray pops out. Make sure the SIM card is seated properly in its tray and then reinsert it carefully.
For more detailed instructions, here is how to remove a SIM card from an iPhone and here is how to remove the SIM card from a Samsung phone.
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Carefully clean the SIM card
If simply reseating the SIM card didn't do the trick, your phone might benefit from ensuring the card is clean and the contacts are clear. Remove the SIM card from your phone, carefully extract it from the tray and then use a microfiber cloth to wipe away any dust, dirt, or debris. A can of compressed air can help blast away any grime, but don't get the SIM card wet — always use a dry cloth.
Try the SIM card in another device
If you've restarted the phone and the card has been cleaned and reseated, it's entirely possible there's something wrong with the SIM card. The easiest way to find out? Install the SIM card in another device and see if it works there. You'll need to test it in an unlocked device, or a device that works with the same cellular carrier as the SIM card you're testing. If the SIM card works, it's probably an issue with your phone rather than the SIM card.
If that's not an option, you can try the opposite test: Put another device's SIM card in the phone that's not working and see if the problem persists. If it works, then the SIM card is to blame, not your phone.
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Update your carrier settings
It's possible that your phone's carrier settings might be to blame, especially if your cellular provider has recently updated its configuration and the changes update automatically on your phone for some reason.
If you have an iPhone, start the Settings app and then tap General, followed by About. If there's a carrier update available, you'll be prompted to install it now.
Like iPhone, Android phones should update carrier settings automatically — but if something goes awry, not all versions of Android OS allow you to update your carrier settings manually. To check your phone, start the Settings app and then search for Carrier Settings. If you have that option, tap Update Profile.
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Reset your phone's network settings
If you're still offline, try to reset your phone's network settings. Treat this as a last resort, because it will also reset your Bluetooth paired devices and Wi-Fi network passwords. But if your SIM card is still not working, it might be worth the inconvenience.
On the iPhone, start the Settings app and then tap General, followed by Transfer or Reset iPhone. At the bottom of the screen, tap Reset, then Reset Network Settings.
On Android, start the Settings app, then System. Tap Reset options, then Reset Wi-Fi, mobile & Bluetooth.
Freelance Writer
Dave Johnson is a technology journalist who writes about consumer tech and how the industry is transforming the speculative world of science fiction into modern-day real life. Dave grew up in New Jersey before entering the Air Force to operate satellites, teach space operations, and do space launch planning. He then spent eight years as a content lead on the Windows team at Microsoft. As a photographer, Dave has photographed wolves in their natural environment; he's also a scuba instructor and co-host of several podcasts. Dave is the author of more than two dozen books and has contributed to many sites and publications including CNET, Forbes, PC World, How To Geek, and Insider.
