This method is exactly what is being sold on Ebay for £1.00+
If you have a UK Vodafone Samsung Z540 (Z540v), you can bypass the Network lock.
First of all remove your sim card from the phone.
Switch on the phone.
Key in: *7465625*228#
Switch off the phone.
Insert the sim card of your choice and switch your phone on again.
Your phone should now be accepting your sim card.