Currently have the i6. Can't use it much as my wife loves it and keeps it n her hands whenever we leave the house. She has always preferred a NON smartphone. So, I'm thinking, use her upgrade to order an i6 Plus. She does not want a Plus. I think I do. So the plan is get the Plus and swap the SIM cards. Is this going to work? Does the account and phone number follow the SIM? Or, does it all follow the IMEI?