Sim Card Invalid Error on Factory Un-locked iPhone 4S

I brought 2 iPhone 4S from Singapore and shipped to India for my brother and his friend. Apple Iphone always having trouble with network carrier if it is not factory Unlocked. So, I buy both Factory unlock iPhone 4S. However, got network problem with one iPhone 4S. My problem is one iphone 4 is perfectly working with Indian carrier and another cannot identify the Sim card. It shows sim card is Invalid. I remove the sim card and insert it again but cannot solve the problem. Even I tried different sim card but cannot solve the problem. I checked same Sim card is working perfect in one iphone and not in second one. I don’t understand why is not working in one phone. Anyone have any idea to solve this problem then please help.

I also have Apple iphone 4 which I brought before few months. I think your problem your one phone, it is not unlocked properly. If it is not purchased from genuine Apple retailer than that kind of problems occurred. So always buy iphone from Apple store only. You can check the same on official site of Apple that your existing phone is a genuine copy or fake.

Thank you for your Instant reply. I had brought it both from Apple Store only. It is a original product. Both have same model No means so if one is unlocked then another one also must work. What can be the actual issue behind this.

I think it is some internal hardware problem and doesn’t recognize your sim card properly. You have to contact to Apple store from where you purchase this phone and talk to them about this problem. I hope they might help you to come out this problem. Sometimes they replace the phone if problem is not solved.

I got this same problem in Apple Iphone 4. I brought Apple iPhone 4 from Apple store. It is factory Unlocked and all is working fine. But before a few days I upgrade the firmware to iOS 5.1 and after that sim card is not detected by phone. It shows sim card is not valid and no service is detected by the phone. I tried many times to insert the sim card but cannot solve the problem. I brought this phone from UK only however network problem is occurred. Anyone have any solution for this problem because I don’t want to ship it back to US. Please guys need a help.

It is not hardware problem. This problem occurred because of software upgrade. I also got this problem in iphone 4 after upgrading to iOS 5. It has lots of Bugs and many people got this problem after upgrading to iOS5. I restore my phone and downgrade the OS to ios 4.3 and now my sim card is working fine.