I have an SE running iOS 18. Earlier today, I tried to make a phone call, and Siri said something like cannot find a connection. I have never run into that before. After a lot of searching, the website for my carrier told me what to do. go to settings, cellular, and find cellular data. Turn that off and back on. Also, if you have a setting that says something like use this line, turn that off and back on also. That seemed to reset things, and everything is working fine now.