How to Unlock Your Phone if it is Locked to a Specific Network

Most websites will charge you to unlock your phone, but you can actually do it for free on one of these 3 websites:
http://www.unlockitfree.com/
http://www.trycktill.com/eng/unlock_swe.asp
http://www.nokiafree.org/ (not just Nokia, but a few other brands as well)

Or you can try with this paid one, seems to be way more cheaper than the other ones around http://www.mobileunlockstore.com/

Have your IMEI code ready by typing *#06# on your phone, the IMEI code will show up on screen.

Remember, by unlocking some phones you may be in breach of a contract between you and your service provider. Please note that it is not working for all countries.