Assuming I am on a family plan with Tmobile and am thinking about jumping ship to AT&T or Verizon. Assuming that there is only a single iPhone on the entire family plan, rest is no data, just voice only with text, is it cheaper for just myself to hop over to AT&T or Verizon and have the rest of the family stay on Tmobile? Or is it cheaper for the entire family to get new phones from AT&T or Verizon? If cheaper to have entire family on it, is it possible for me to get an iPhone myself from Apple.com, then add the other lines in and convert it to a family plan a few days after purchasing the iPhone? In either case, is the cost of an iPhone reduced when being on a family plan compared to a single-line iPhone plan? Any numbers would be great!