The U.S. Justice Department approved the merger between satellite radio companies Sirius and XM Monday, more than a year after the two companies first announced their deal.

But for fans of Howard Stern, Opie & Anthony and other Sirius and XM on-air personalities, there are still many questions about how much a combined Sirius-XM service will cost and what programs they’ll be able to hear. Plus, Sirius and XM face one more regulatory hurdle before the deal can officially be completed.

In its decision, the Department of Justice determined that an XM-Sirius merger was not anti-competitive. The Justice Department argued that other media companies such as Clear Channel (CCU, Fortune 500), CBS (CBS, Fortune 500), or even Apple (AAPL, Fortune 500) with its iTunes software and iPod music player served as alternate options for music and media customers.

The Department of Justice did not place any conditions on the merger.

“Since we determined that there was no competition between the companies, we did not need to set any conditions as such,” said Assistant Attorney General Thomas Barnett during a conference call with reporters Monday afternoon.

But the Federal Communications Commission must also approve the deal. The FCC has yet to make a decision on the merger and it could decide to place conditions on the deal. A spokesperson for the FCC was not immediately available for comment.

Since Sirius and XM are still awaiting approval from the FCC, it is unclear exactly what a merger would mean for consumers. Both companies charge their customers a $12.95 per month subscription fee for their most basic packages. Some have feared that if Sirius and XM are allowed to merge, the two companies would raise the monthly price.

However, the companies said last year that they would be willing to offer a so-called “a la carte” price plan where consumers could pick certain packages for less money.

The merger would combine the nation’s only two satellite radio companies and create a company with about 14 million subscribers. It would bring together Sirius’ most well-known content, including shock jock Stern and National Football League games with XM’s Major League Baseball as well as programming from Oprah Winfrey.

Currently, subscribers for either Sirius or XM can only receive broadcasts from one of the two services with their satellite radios. But in a statement Monday, XM reiterated that radios owned by its current subscribers would not need to be replaced in order to continue receiving programming.

Shares of XM (XMSR) and Sirius (SIRI) both rose after the announcement.

Losses are narrower-than-expected loss on Thursday as it added more than 1 million subscribers during the quarter that included the holiday season.

But the results failed to excite investors who have been waiting more than a year for regulators to approve XM’s plan to be acquired by rival Sirius Satellite Radio Inc (SIRI.O: Quote, Profile, Research). The proposed deal was first announced in February 2007.

XM reported a fourth-quarter loss of $238.8 million, or 78 cents a share, compared with a loss of $263.2 million, or 90 cents a share, a year earlier.

The loss includes 25 cents a share in merger and settlement related charges, XM said. Excluding those charges, its loss was 53 cents a share, better than the average analyst expectation of 63 cents a share, according to Reuters Estimates.

U.S. regulators have yet to decide whether to approve the XM-Sirius deal. They include the Federal Communications Commission as well as the Department of Justice, which will decide if combining the two U.S. satellite radio companies would be anti-competitive, as some critics have charged.

Analysts’ opinions about the potential success of the deal have been mixed. Several have recently said they are now more optimistic, while other remain skeptical.

“Since the one-year anniversary of the deal has passed with no word from the DOJ, risk continues to exist that the deal will not happen,” Barrington Research analyst James Goss said in a client note earlier this week.

On a conference call with analysts, XM Chief Executive Nate Davis said the company does “continue to look forward to a positive resolution to this matter soon.”

In yet another coup for the burgeoning high-definition DVD format, online DVD rental service Netflix Monday said it will stock high-def movies exclusively in Blu-ray.

For Netflix, that means no more discs in HD DVD, the format spearheaded by Toshiba. Netflix has been stocking high-def movies in both formats since early 2006, but said in a statement that all of its new high-def movie purchases will be Blu-ray and that it will phase out HD DVD discs by the end of the year.

Netflix made its choice after watching several major studios side with Sony-backed Blu-ray. Warner Bros. Entertainment in January said it will put out high-def movies exclusively in Blu-ray, joining Metro-Goldwyn-Mayer Studios, Sony Pictures, Twentieth Century Fox and Walt Disney in the Blu-ray camp. Two major studios, Paramount Pictures and Universal Studios, have sided with HD DVD.

The rental service said that only a portion of its subscribers choose to receive high-def movies. To put it in perspective, Netflix says its library includes more than 90,000 DVD titles, with only 400 of those in Blu-ray.

But that’s hardly the point. The main reason for Netflix’s decision seems to be its desire to get this format war over quickly so that people will start buying high-def gear. After all, what retailer (or DVD renter) wants to have to stock two HD versions and a standard-def version of every movie title?

“The prolonged period of competition between two formats has prevented clear communication to the consumer regarding the richness of the high-def experience versus standard definition,” said Ted Sarandos, chief content officer for Netflix, in the statement. “We’re now at the point where the industry can pursue the migration to a single format, bring clarity to the consumer and accelerate the adoption of high-def.”

Some have already called this fight in Blu-ray’s favor. One thing’s for sure, it’s come out swinging in 2008.