What is the unlock code for the Sony Ericsson W200a?

If you're referring to the phone lock code, it could be 0000 (4 zeros) or the last 4 digits of your phone number. If what you need is the code for carrier unlock, you can get the code from phone unlocking websites such as unlocktotalk.com and mrunlock.com. You just need to provide them with your carrier and IMEI. It's not free but it's not expensive either. It will cost you less than $20.

Get the unlocking code for your mobile from prounlocking.com .
Once you get the code, you may follow the instructions at http://www.mobileunlockguide.com/ .This will help you to unlock your mobile easily.