Mobile phone advice please... switching providers

Mrs mememe is moving from O2 to Vodaphone but keeping her Galaxy S3 phone.  She's got a PAC to move the number, no problem.  But when I put the Vodaphone SIM card in I found that I needed a network unlock code.
Painful getting one from O2 ... will take 7 days!! In the meantime Mrs mememe has no phone as O2 contract has been cancelled.
Surely it must be illegal to have a lock code on a phone that Mrs mememe bought 2 years ago from O2 when she took out the contract, then fook about and make it hard to get an unlock code.
Akin to buying a BMW, then 3 years later having it serviced at a Ford dealer and BMW disabling the engine management system so it doesn't work.
Anybody else had mobile switch problems?