Can I have a SiM sent to NZ, unlock it when I go to France (or In NZ before I leave) and then use in Britain afterwards?

You need to make sure your handset is unlocked before you travel, not the SIM. We can send the SIM to NZ - delivery options are displayed at checkout. The global SIM would be best for use in France and UK.

HI you can use the sim in both countries only if the phone in which you are going to use your sim is unlocked from network .Else if its locked to any network provider then unless you unlock it you cant's use your french sim in it .To unlock mobile phone visit Unlock-Free.com here they generate unlock code for some older mobile models at free of cost .