What exactly do you mean by the SIM locking?
SIM PIN locking is enabled on new SIMs by default.
But you can disable it if you don't want it.
You only have to enter the PIN when the phone is switched off and then on again - i.e. when the phone reboots.
Are you saying that you are being prompted for the SIM even when you do not reboot your phone?
Maybe your phone is crashing and rebooting unilaterally?
Hope this helps.
