Branded K500i freezes with different SIM

Posted by TheOddish
I just bought a K750i, so I thought I'd give my old K500i to my mom, but when I put her SIM card in the phone and start it up, it completely freezes after about 5-10 seconds. The phone is branded (Telia) and it works fine with my Telia SIM, but mine is a subscription plan and her's is a Telia cash card (don't know the english term).

Does anyone have any idea what could be the problem?

Posted by TheOddish
No one has any idea what could be causing this?