If you're experiencing glitches and lag on your cellular network connection after updating to an iOS version past 18.2, it's likely due to a bug in the new software that could be affecting cellular data handling, potentially causing instability in network connections, especially in areas with weaker signal; try restarting your phone, checking for carrier network updates, resetting network settings, and contacting Apple Support if the issue persists; Threads regards the issues https://www.reddit.com/r/ios/comments/1fj6ae3/anyone_else_got_really_slow_mobile_data_speed/?rdt=55290 https://discussions.apple.com/thread/255763551?sortBy=rank Settings to try People said it was because of RCS in the new update. Don't worry though, in iOS 18.1 Beta 5, they mostly fixed the issue. It is still a little slow, but at least it's usable. For now, turning off RCS should fix the issue. To turn off RCS, go to Settings > Apps > Messages > RCS Messaging then turn off the RCS Messaging slider. Also try to reset try to go to Cellular>and reset Cellutar usage statistics and check Disable background app refresh. Head to Settings, then General, and tap Background App Refresh to switch off unnecessary apps. Threads regard how to improve you iphone https://www.magfone.com/repair-ios/ios-18-bugs-fix.html, Conclusion: I call apple, they run diagnostics didn't fix, but I suspect their updates, after ios 18 and ahead, my wife has same issues in 2023 the board has iphone system board has to be replaced, i did also called t-mobile and they done they work, but I still have the issues. I'm really frustated not been able to use applications like google voice, or facetime audio to call people without braking voice, failing to retrieve data, so just finish paying off my phone from carier is a iphone 14 plus, excellent conditions but not celluar network connections stable, also did pay apple care for 2 years and right after cancell the payments with update it has that issues. Relly frustated with apple, it never has issues while Stive Jobs was in charge, I looks they loose track of having realible phones and software