I think your blackberry didn't recognize your previous password, it's happened because you upgrade your os when your phone still have active password. Use your PUK code to unlock blackberry curve 8520 password, just type any password until your phone asking you to enter puk code. PUK code can you found from your sim card bundle if you don't have it just call your service provider, they will give it to you. After you put that puk code your blackberry unlocked from old password.

Hello,

the truth is that you can unlock the phone ,but you can't unlock all phone for free.

The payment sites are very cheap you could try it out and see.

You can the link below to unlock .

Note: unlock is not free, You will be charged to get your unlock code.

The only way by which you can get the unlock code for free is by calling your service provider

and requesting for your unlock code.

If you service provider refuses to give it to you, then there is no other place where you can

get a free unlock code.

Visit the link below if you are interested in buying the unlock code:

(mobileunlocked.com/mobile_unlocking.php)

Good luck.