How do I swap the content of two phones
As both phones are identical (make that sure first!), there's even a possibility to "cross-clone" them:


First you'll need a custom recovery such as clockworkmod or twrp. Other than "stock recoveries", custom recoveries support...
nandroid backup: Using your new custom recovery, you can create a Nandroid backup of each device – which basically is a collection of "drive images" from all the partitions the device has. They will be stored on your SDCard usually.
Now swap the SDCards, enter the custom recovery again, and restore the Nandroid backup. With this step, the "body switch" should be perfect :)