I have two older iPhones and use the same SIM card in both. My newer, preferred phone recently started getting terrible cellular data service, even in places where I know coverage is strong. When I move the SIM into my older, somewhat damaged phone, the connection works normally and shows full or nearly full bars. The newer phone worked fine for about a year before this started, so I'm confused about what could have changed and how to troubleshoot it.
2 Answers
The issue could be related to the newer phone’s supported cellular bands or network technology. If it can’t connect properly to a band your local towers rely on, it may perform worse even with the same SIM. Check that both phones support the same LTE bands and carrier settings, and make sure the newer phone is updated and properly unlocked.
Since the SIM and service work normally in the other phone, the problem is probably with the newer iPhone rather than the account. A damaged or loose cellular antenna, especially if the phone was recently repaired, could cause weak data performance. I’d try restarting it, installing any carrier or iOS updates, resetting network settings, and testing it outdoors. If that doesn’t help, have the antenna and modem checked by a repair shop.
I’m not holding it in any unusual way, so that probably isn’t the cause. I’ll try the network reset and have the phone inspected if it still acts up.
Both phones are older models from before the iPhone 11, and the newer one worked perfectly with this SIM for about a year before the problem began. That’s why I’m wondering if it might be a hardware or settings issue instead.