If I were to buy a phone from Vodafone, could I use an Orange Sim Card in it?

If it had to be unlocked, how would I do this?

Thanks in advance
-MIML

Yes, you can approach Unlocking4free.com where hey offer free unlock codes for certain old models or Wickedunlock.com and remove the network lock with Vodafone.Once unlocked you can use it with other GSM networks.