Make sure the sims are exactly the same bit.

Hey this hyfeno.com/how-to-unlock-gsm-phone/ explains a lot about unlocking phones and the security codes on them. It even has some instructions for your Nokia phone, check it out.

Hi all,

I have a bit of a problem involving my old Nokia 6103b. I no longer use this phone,
but I wanted to give it to my mother in law. Problem is when I insert her sim card
the phone wants me to enter the security code. I don't recall ever changing it from
the default code. However, when I insert my sim card the phone works and does
not ask for the security code. Both sim cards are active with Rogers wireless and
work in other phones. Any help would be greatly appreciated. I should also mention
that I tried the master code generator where you enter the phone's serial number.