A look at the Hong Kong PSN website shows the Flashback Map Pack #1 listed for release on the 17th of January. This adds up with the comments made by ND on their 1.03 patch post, stating “Full details on the DLC content will be posted by January 17th”.
Here is a screenshot in case the page gets taken down:
Players who have downloaded the 1.03 patch will also notice the 4 new maps in the custom game list, however you can’t actually play them until the pack is released and purchased/downloaded. The pack includes 4 Uncharted 2 maps, being the Sanctuary, Caves, Fort and Lost City.
Credits to ND forum user Da_Chimp96.