My sister has an iPhone, but no data plan. So, if she's out and I want to text her from my iPhone, she needs to make sure she doesn't have iMessages running on her computer at home. If it's on, I text her a bunch of times and I just get the blue bubbles. Then I get a bunch of SMS messages from her saying "where are you? why aren't you texting me back" and hilarity ensues. I guess I could just call her.