Two words you never want to see on your iPhone, especially when you're in a familiar area, are "no service." Several things can cause a no-service warning, but if you get the warning after inserting a new SIM card, the card itself could be the culprit. Fortunately, there are a few things you can try if you get a new SIM card no-service warning.
Basic iPhone No-Service Troubleshooting
Usually, if you get a no-service warning, it's a sign your phone isn't picking up a signal from a cellphone tower. If you get some type of "iPhone network not available" message after inserting a new SIM card, pop the card out and insert it again. Do this by pushing the end of a paper clip into the hole on the side of the phone, which pops the card out so you can push it back in. After you reinsert the SIM card, restart the phone and see if you still get the new SIM card no-service message. If so, it could be a problem with either the card or the account.
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Update Carrier Settings
The iPhone network not available issue could be related to a software incompatibility. Check to see if your phone has an operating system update that may fix a bug that causes your phone to register an iPhone no-service warning. You can check for updates by going to "Settings," "General" and "Software Update." If you see one, download the update. After you update or if your phone is already up-to-date, also check for a carrier settings update. You can find this under "Settings, " "General" and "About." Pause on this screen for 10 seconds or so to see if an update alert pops up.
Update Network Settings
Another fix for the new SIM card no-service problem can be to update your network settings. This clears out any old settings that may be causing the iPhone network not available warning. Go to "Settings," "General," "Reset" and "Reset Network Settings." You need to press "Reset Network Settings" to confirm. If after doing this, you still get an iPhone no-service warning, contact your cellphone carrier. Something may have happened on the carrier's end that requires a technician to check a box or make a couple of changes to have you up and running again. There could also be a temporary outage in your area that coincided with your new card installation. Either way, your carrier can help you figure out what's going on.