I'm pretty sure they will only allow this once the contract has finished - could be wrong - but that's my understanding
Hello Mr. McCrum,
I like to inform you that we're unable to provide the unlock code for iPhone as it is exclusively locked by Vodafone.
I'm sorry that I'm unable to provide unlock code lfor iPhone
Trust this helps.
Kind regards,
Rohit Sarode
Vodafone Customer Services

has your contract finished ?
Vodafone only started supplying iphones in January