Hello, I'm thinking of calling three to unlock my iPhone 4s. I'm going on holiday and want to use a Sim from another carrier with a better data roaming package. If Three unlock my phone and I then use another carrier's Sim for a week, when I'm back in the UK can I just go back to my normal Three sim or will the iPhone be locked to the provider I changed to when abroad? Does that make sense? I hope someone knows the answer Thanks in advance.