I am dealing in SIM cards, Some of our SIM cards are giving Insert SIM on Nokia1100 suddenly,

After restarting the handset SIM works fine but after the useage of few hours it is again giving the insert SIM. Then again it is working fine after restarting it is working fine and again insert SIM.

I have checkd the SIM cards in other nokia phones and working fine all the time.

Can you please let me know what could be the reason for this.

Best Regards,
Vikas Phogat