This is just from what I've read and been told by Gree support on my recent transfer.
I've read that Apple does not want to allow UDID association with apps. Who cares why, but I think this is the reason that the 'in-game' transfer process doesn't work anymore. i.e. click transfer > old device and then on new gadget tap transfer > new device (although I have got this to work about 1 year ago).
Anyways, I spent the last 2 weeks getting a character transferred over. The process is to back up your old device to iTunes or iCloud. Then on the new device, restore from that same backup. When you open the game on the new device, you will be prompted to restore data; click yes.
I hope this helps people with future transfers.
larrydavid inc has no liability for lost games and default emails from Gree.