My friend gave me her old cell phone but there's a lock code on it that she does not remember... How can I reset the phone so it will delete the securtity code?

What's your Phone brand and model?If your phone is nokia phone,You can try 1234 or 0000 if these codes does not works,
You can use the master reset code and reset from the code lock...
You can get the Free Nokia DCT phones master reset code and Alcatel Phones old Master Reset code at Unlocking4free.com/unlock-your-phone
and reset from security,password lock..

Have you tried another sim card? Maybe it's just the sim card that's locked

You need to doing hard reset to make your samsung jet s8000 unlocked from your old password. Follow this step to unlock samsung jet s8000 password and reset it to default factory setting :
1. Press Menu.
2. Press Settings.
3. Press Reset settings.
4. Press All or the settings you want to reset.
5. When the box next to a menu item is ticked (V), the setting will be reset.
6. Press Reset.
7. Key in the phone lock code and press Confirm.
8. If it is the first time you use the phone lock code:
9. Key in the phone lock code again and press Confirm.
10.Press Yes.
But remember that method also wipe out all your previous data in that phone.

Get him to take it back to his provider for you and they will reset it.

the security code is the last four numbers of your phone number or whatever phone number is programmed into the phone.

This link will help you to calculate lock code with imei no.http://www.nokialockcode.com/calculate.php.Rate me if it was helpful.

here are some codes to get u started

*2767*3855# = Full Reset (Caution every stored data will be deleted.)
*2767*2878# = Custom Reset
*2767*927# = Wap Reset
*2767*226372# = Camera Reset (deletes photos)
*2767*688# Reset Mobile TV

problem not clear

you need to take it to repair shop to unlock it this is the only way ......sorry