Quick question. Me and my sister have IPhones on a family plan. I have a 4s and she has a 4. My sister's phone is eligible for an upgrade to the 5, where as I have a couple of months wait until I can upgrade. My sister isn't concerned with having the latest and greatest iphone, where is I'd like to upgrade. Can I have my sister's phone upgraded and swap SIM cards so I can use the 5 and give my sister my 4s? I wouldn't be changing plans at all, so that wouldn't matter. This would also make it possible to upgrade the 4s to a 5s and swap back, if apple brings out a new iPhone this fall. If anyone has done this, I'd appreciate any help. Thanks.