unlocking code for samsung x640?

I want to unlock a new (second hand) phone from a network. I need a code. Have searched the net and found some sites. Most want to charge you. Some say free but I dont feel comfy putting my phone number on their sites. I have asked the network its locked to and they say up to 10 days as they need to get code from manufacturer. I did fine a code in a forum. I'm not sure if i try it will it stuff up my phone? Its only numbers. Would somthing happen if i put random numbers in when its asking for the code?

Somone asked about the same thing on here and one reply was that all phones have a different code...is this true?

ANY HELP APPRECIATED!