Nokia is offering Windows Phone Store credit and a series of Gameloft titles to Lumia owners in a seemingly global campaign dubbed "World of Entertainment."
Depending on where you're located, the amount of Windows Phone Store credit being offered changes. For example, residents of the UK are being offered £34 worth of games and £20 of Windows Phone Store credit, whereas Australian residents are being offered $25 worth of games and $40 worth of Windows Store Credit. Residents of the US are being offered $40 worth of games, and $25 worth of Windows Phone Store credit.
Unfortunately, the Lumia phones that are eligible for this promotion are also location-dependent. In the UK and Australia, the promotion extends to owners of the Lumia 625, 1020, 1320 or 1520, however in the US the promotion is restricted to users of the Lumia Icon, 1020 or 1520 only. The Terms & Conditions also specify that its for "new" owners, however phones purchased from as far back as December are reportedly being able to claim the voucher. Whether or not this is a bug, or just a poorly worded T&C, is yet to be known.
The credit can be used for either apps from the Windows Store, or content from Xbox Video. It appears to be a worldwide campaign, so it does not just apply to the countries listed in this article. In order to redeem the voucher, go to the Nokia Collection in the Windows Phone Store and download the Gift Voucher app. You can then follow the instructions in the app to redeem your gift card.
UPDATE: It may or may not work for existing Lumia owners. This may be based on whether or not you have participated in a free Windows Phone Store credit promotion before.