How to Fix iPhone 4 No Signal Issue on iOS 5.1.1
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sambecket • November 22, 2013 at 4:42pm
I have an iPhone 4 running iOS 5.1.1 (build 9B208) with baseband 04.12.05, but I am getting no signal. How can I resolve this issue?
Answers
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iClarified • January 14, 2026 at 3:42am
A No Signal issue on an iPhone 4 with baseband 04.12.05 is typically caused by a carrier lock or a software activation error. Because baseband 04.12.05 cannot be unlocked using software tools like Ultrasn0w, you must use a SIM card from the original carrier or obtain an official IMEI unlock. To troubleshoot, first try resetting your network settings by navigating to Settings, General, Reset, and then Reset Network Settings. If the problem continues, perform a full restore of iOS 5.1.1 using iTunes. If you are attempting to use a different carrier, you must contact the original service provider to request an official unlock, as there are no functional software unlocks for this specific modem firmware version.