Divachick, if it is your security code for the phone (default 12345) that you have changed and forgotten then you will need to have your phone flashed by a Nokia Service Centre. I cannot see where the PUK2 code comes into this. As previously stated by someone else PUK codes are related to your sim card, PUK2 being to unlock a sim card that has been blocked by entering incorrect PIN2 code too many times. PIN2 is normally used for advanced sim card features like Call Barring services. Personally I feel that if your phone is askng for PUK2 then either yourslf or someone else who has had hold of your phone has played about with security settings and blocked PIN2. O2 will have to give you this code. Take note also that if you enter 10 wrong PUK2 codes then your sim card will be destroyed !!!
Taffytafftaff, I beg to differ. If asim card has become blocked due to too many (usually 10) PUK codes being incorrectly entered then the card has been destroyed and cannot be unlocked by the networks. If you convince the network that your sim card has become faulty rather than blocked then they may replace it for you but noe of the networks will even offer to un-block a blocked sim because they cannot do it