Facebook and Britney Spears launched a premium line of virtual gifts inside Facebook that made several custom designed, limited edition Britney-themed gifts available to users.

The gifts, titled “It’s Your Birthday,” “Britney Pride,” and “Slave 4 U,” etc., cost 20 Facebook Credits each. That’s currently the equivalent of USD $2.00, or twice the price of most Facebook virtual gifts. The gifts are still available today, and may be for some time.

Since the campaign launched, many other artists have expressed interest in getting into the Facebook gift shop. Facebook won’t say how many of the gifts have been sold so far, but a Facebook spokesperson did tell us that the company will “continue to explore licensing gifts, such as the Britney Spears line, and others such as gifts specific to charities.” Facebook also regularly runs sponsored virtual gift campaigns as part of its core offering to brand advertisers.

The Britney Spears experiment is just one of the many virtual gift shop tests Facebook has been running recently. Last week, Facebook confirmed to us that it is now testing the availability of both third party virtual gifts and third party physical gifts with a limited number of users. It’s the first time items from third party merchants have ever been made available in Facebook’s official virtual storefront, though third parties have been delivering a variety of virtual gifts in Facebook Platform applications for a long time.

We think Facebook is likely to continue testing licensed virtual gifts with more musicians and artists whose revenues are increasingly being derived from merchandise sales. Just as fans are willing to pay a premium for officially licensed physical gifts and decorative items, the same will be true for virtual gifts inside Facebook. Since margins are so high on virtual goods, Facebook is in good position to explore several different licensing models while reaching a uniquely large and targeted US and worldwide audience.