I just read the rebate again, and it doesn't say to include your invoice, but I wonder if Nokia has a way to track the UPC code tied to your Amazon account pre-order date??
Please keep a copy of your submission for your records. Mail-In Form, dated store receipt and UPC/barcode panel must be postmarked by January 8, 2010 and received no later than January 15, 2010. Submissions postmarked after January 8, 2010 or received after January 15, 2010 will not be accepted and are void.