Hi. Follow this link to unlock your phone.
http://m.vodafone.co.uk/mobile/help/network-unlock-code/index.htmIf you stay with Vodafone contact them via 191 or livechat and they will be able to switch you to a sim only deal (providing you pay any early termination fees there may be).
If you want to change provider again contact Vodafone and request your PAC and then give that to your new provider and your number will be switched to that network. The PAC is valid for 30 days, after that if its not used you need a new one.