Basically I have ordered my iPhone 4S and currently have an iPhone 4. I am passing my iPhone 4 onto my girlfriend and my iPhone 4S is direct from Apple (so is unlocked).
I have 2 microsims here already. I am going to activate one next week sometime, one it has been activated can I then activate the other one in the same phone, and once that has been activated take it out and then just put it back in Christmas day when I give her the phone? Or does the SIM have to be inserted into the phone at all times? Also, can I activate the sim on my iPhone 4 and then put it straight into my iPhone 4S and it will still work (I know I will still have to enter the APN etc)