Nokia 6510 security code

I recently purchased a brand new Nokia Model 6510 with Serial Number: 350697404381369. As instructed in the manual I changed its manufurer's security code (12345) to my personal number and set the security level at the phone level. What surprises me is that when I insert a foreign sim card, I am not prompted to enter a security code as was the case when I used to own Nokia Model 8210. What is wrong? Is there a way I can activate the phone security code to be functional? I am just worried that my phone is insecure. Further to this problem, the phone does not have the third font size option stated in the manual (instead it has 2 sizes and these being Small and Large). Why is there such a discrepancy? Nevertherless, the latter is not as crucial as the previous problem of the security code failure. Kindly assist on how I can go around solving this problem. Should I return the hand set to the dealer or is there a code for activating the phone security code.

Sincerely

E. E. Maeda, PhD
Associate Professor in Nutrition and Food Sciences.