Is your iPhone not connecting to cellular after installing iOS 17.2.1? This might help
UPDATE January 3, 2024: During a conversation with a couple of readers affected by this issue, I suggested trying to install the iOS 17.3 public beta, and in both cases this appeared to solve the issue.
If you're affected by this bug and would like to try this, here's what you need to do (bear in mind that this isn't a confirmed fix and that beta versions of iOS may be buggy and cause other problems):
In a browser, go to beta.apple.com, click on the sign-up button and sign in using your Apple ID and password.
On your iPhone, tap on Settings > General > Software Update and then on the Beta Updates. Select iOS 17 Public Beta and the latest iOS 17.3 public beta version will be available to install.
Selecting iOS 17 Public Beta on the iPhone.
That mysterious iOS 17.2.1 update released just before Christmas seems to be causing havoc for some iPhone users.
A couple of readers pointed me to a thread over on Apple's support forum where users are complaining of having problems connecting to their cellular network following the update.
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The problem seems to affect calls and data, and while the majority of complaints appear to be from T-Mobile and Verizon customers, the problem doesn't seem limited to these networks.
Forum users have offered up a few suggestions, ranging from deleting any VPN profiles off the iPhone (tap Settings > General > VPN & Device Management > VPN, then tap the i next to any VPN profiles and Delete VPN) to resetting network settings (tap Settings > General > Transfer or Reset iPhone > Reset and then tap Reset Network Settings), but these have had limited success, and I believe that these are solving secondary issues, not the issue being caused by the update.
And the majority of affected users don't have a VPN installed.
Bottom line: These are worth a try, but don't hold your breath.
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It's also worth noting that this issue isn't new; I've seen sporadic reports for this on many prior updates. However, this specific iOS 17.2.1 update seems to be creating more widespread issues.
Along with this cellular issue, some users are claiming that the update has adversely affected battery life, while others are claiming that the iPhone overheating issue is back.