(HOW TO FIX) Invalid SIM after updating to iOS 9.3

Before I begin, let me state that this is not a guarantee for everyone's device, but what I have found to correct the phones I have come across.

I work as Tech Support for a major cellular carrier specializing in iPhones. As you can imagine, when a new update is released, I see every problem associated with it. With this iOS 9.3, many have experienced upon restart an "Invalid SIM" message pop up on their screen which will not allow them to continue setting up their device. It also may prompt to contact your carrier for a valid SIM. An iCloud erase becomes impossible due to inability to set up Wifi network or obviously get cellular data. Trying to restore to iTunes normally pops up similar error and won't let you continue. Even putting the phone in recovery mode and successfully wiping and reinstalling software on some of these devices is not working. The phone is basically a brick.

This is NOT a network/carrier issue. These SIMs do work in other phones if you take them out and test them in my experience so far.

While troubleshooting a customer's device, after all the above and more had been performed, it clicked in my head. This customer's phone was still locked to our network, meaning it could not be used or sold to someone to be used with a foreign SIM from another country while traveling or carrier. Having a locked device is completely normal when under contract/installment plan with a carrier. Typically a phone will have to be paid off or have its contract completed for a customer to request from their carrier to unlock the device. Luckily, this specific customer had a phone eligible to be unlocked and since they had just restored their phone (a must for unlocking an iPhone) it was worth a shot. I was able to successfully release their phone to be unlocked, while they would normally complete next by resotring the phone. The customer powered the phone down, back up, and was able to successfully set back up their phone.

So, as it turns out, this new update is basically scrambling with the carrier lock, making it unable to realize it's own carrier's SIM is in fact being used. Until an update from Apple is put out, this is so far the only way I've found to correct it.

Please also note that not everyone's phone can be unlocked from their carrier. Most carriers will require that phone to be off contract, or paid off, either by installment plan or just paying an ETF fee. Some also may require there not be a past due balance on account or other things. Search your carriers website on how to submit a "device unlock request" because every company is different. It may also take 1-2 business days for a request to be approved. Most reps you call into have the power to press a button and release it to be unlocked. This typically goes to an offline speciality team to process. And if you do call into to your carrier's customer service, don't yell at them. They have no control over any of this. If your phone isn't eligible to be unlocked, as of now, you may have to use a temp device until an iOS update fix is released.

Again, I can't promise this will fix everyone's device, this is just what I have personally discovered while troubleshooting this issue. Just wanted to share and help others! Don't shoot the messenger! Good luck! 😉