You can do this!Right, you need to create a folder on your MMC on the 6600 and put all your messages you want into it. Then take your MMC to the 6680 OR a pc card reader and either,
1) Drop the card into the 6680 and simply copy the messages to the new phone, and bobs your uncle...OR
2) Tranfer the message folder to your PC then bluetooth across the messgaes to your 6680 if you have a bluetooth PC dongle of course!
Hope this helps matey.
Thanks
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P.s Ive just tried it and it works, I have a 6600