I’m doing cellphone repairs since the year 1999 and recently came across this problem on a Iphone 4 and would love to share it with you. So a client brought in a Iphone 4 with a charging problem, after replacing the charging flex I note that the phone was searching for network and showing no sim card inserted. I was stressed, strip the phone again to make sure I did not damage the sim reader or antenna plate. Everything looked good. After rebooting the phone still had the same problem.
What Caused this problem.
When you replace a Iphone 4 charge flex you have to remove the battery flex from the connector to release the antenna plate cable. This causes the phone internal clock to reset. The Time and region is now not set correctly causing malfunction to the sim reader and connection software.
1. Quick solution, connect the phone to a Wlan ( Wi-Fi ) Connection this will sync the phone time to your current location and set the time it correctly.
2. Goto Settings -) General -) Date & Time and set the date time and zone manually
3. Turn Phone off and back on with sim card inserted and your problem would be solved.
I really hope this information helps you ! and please give feed back & if you feel generous make a small donation below ;)