Can I change from 02 to vodafone ?

If the phone you buy is unlocked to any network then yes.
What phone is it? Can you link to it?

redcross wrote: »

Samsung Galaxy S advance ,I can't find it online but I have a magazine with offers from Carphone Warehouse and if I buy it from 02 it's only 280 euro compared to vodafone and meteor where it is over 350 euro.

Does this mean it's unlocked ?

If you want to see the true (unsubsidized, unlocked aka SIM-free) price, look up and see what amazon or expansys are charging. If any of the network shops are offering it for significantly less, it's locked to that network.

Edit: Both expansys and amazon are selling that phone unlocked for €310 so the Vodafone and Meteor 'deals' you quoted are crap, try O2 and ask if it's unlocked. If the O2 offer of €280 is for an unlocked phone, you will be able to buy it as an appliance with no paperwork to do with a contract. If they ask you to sign anything, walk.