The "Christmas present for Gran Turismo 5 fans" includes the Lamborghini Murcielago LP 640, the BMW M3 Coupe and, the Jaguar XJ13 will be available free of charge from December 24 until January 31. All three vehicles are noted as "Chrome Line" editions.
Owners of the game's Collector's Edition will recognize the free Lamborghini and BMW vehicles as two of the five bonus rides included in the game's Collector's Edition. The Jaguar had previously been offered via a Gran Turismo 5 Facebook app [via 1UP].
Shacknews has contacted Sony Computer Entertainment of America to find out if a similar offer will be available in other regions and if the bonus vehicles will be offered as premium DLC in the future. At the time of publishing, Sony has not released a comment regarding the content.
I assume we'll be able to download these by using an account registered with Japan as the locale.