Unlocking Xperia x10 using a jacket I have passed the limits for attempting passcode / sim code. Someone has advised me that I should use a jacket to unlock the phone (Xperia X10a)

Where do I get the jacket from? Also, will the jacket solve my problem?
Don't mix things here. From your posts it looks like you have entered your SIMs PIN to often and need now to enter your PUC/PUK. This has nothing do to with your androids phone lock. In Germany it's common practice to receive the PUK together with the SIM card. If you have no PUK you can only ask your SIM provider for the PUK or a new SIM. I am not aware of any other method to unblock a blocked SIM.