I am trying to understand how this works with the iPhone. My daughter and I both have iPhone 4s. When she was in London and i was in the us, we texted. When she was connected via wifi the dialogue boxes were blue (iMessage) and when not they were green (SMS). She was not using a local sim (we are on Verizon). Recently, she went back London and Madrid. Got a local sim in London. I started receiving iMessages from her apple id. Ok, no problem. Now that she is back in the US, I have two conversations going. Now when I text her from our original thread it is green and I have to use the thread started while she was in London if I want it to be blue. On her end it is all iMessage (blue). Is it because that my phone now "knows" her apple id it can differentiate and does so? Thanks for any insight. Obviously, this is not a problem, I am just trying to understand what is going on.