My iphone 4 shows sim failure and then invalid sim, what should i do?

Get a new SIM card it won't change anything i your phone and its free to get a new SIM card. Trust me ive had the same thing happen to my phone

Shani said:

My iphone 4 was running on ios 5 and when i updated my iphone 4 to ios 6.1.3, i lost my network. I also tried reset network settings but it was useless!!!

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Your phone says "Invalid Sim" that means your phone is locked to particular network. To solve this problem, your need to get your iPhone unlocked.. You can get it unlocked your iphone4 from Network lock safe and securely using Remote unlocking method from the site Mobile-Unlocker.com