How do i unlock the security code on my phone?

i bought a cell from a friend and when i got it home and i changed my sim card the phone is security locked and i cant get into it and i was wondering if there is any easy way or any websites that i can go to that will help me fix my problemHow do i unlock the security code on my phone?
The service provider cannot help you. It is not called a security code for no reason. You have 3 choices:

1. Replace the device

2. Send the device back to the manufacturer or take it to a shop to have the software flashed and reloaded

3. Start at 0000 and keep adding 1 to it (0000; 0001; 0002; etc) until you hit the right numberHow do i unlock the security code on my phone?
Go to the ATT store with your friend and they will unlock it for you. Or your friend can give you the unlock number (usually available on his web account with the mobile company)