Hi We're about to go on an International trip and I will be taking my iPhone with me. Can I use iMessage without incurring any charges (AT&T)? if I'm right I can't turn on airplane mode otherwise SMS will not work. So if I turn off network, data roaming, fetch but keep wifi on, can I use iMessage for free? I just want to be able to message family and use face time to talk to them each night. Thanks much!