FILED PURSUANT TO RULE 425

Filed by Sirius Satellite Radio Inc.
Pursuant to Rule 425 under the
Securities Act of 1933 and deemed filed
pursuant to Rule 14a-12 under the
Securities Exchange Act of 1934

Subject Company: XM Satellite Radio Holdings Inc.
Commission File No.: 0-27441

This communication contains “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements include, but are not limited to, statements about the benefits of the business combination transaction involving Sirius Satellite Radio Inc. and XM Satellite Radio Holdings Inc., including potential synergies and cost savings and the timing thereof, future financial and operating results, the combined company’s plans, objectives, expectations and intentions with respect to future operations, products and services; and other statements identified by words such as “anticipate,” “believe,” “plan,” “estimate,” “expect,” “intend,” “will,” “should,” “may,” or words of similar meaning. Such forward-looking statements are based upon the current beliefs and expectations of SIRIUS’ and XM’s management and are inherently subject to significant business, economic and competitive uncertainties and contingencies, many of which are difficult to predict and generally beyond the control of SIRIUS and XM. Actual results may differ materially from the results anticipated in these forward-looking statements.

The following factors, among others, could cause actual results to differ materially from the anticipated results or other expectations expressed in the forward-looking statement: general business and economic conditions; the performance of financial markets and interest rates; the ability to obtain governmental approvals of the transaction on a timely basis; the failure of SIRIUS and XM stockholders to approve the transaction; the failure to realize synergies and cost-savings from the transaction or delay in realization thereof; the businesses of SIRIUS and XM may not be combined successfully, or such combination may take longer, be more difficult, time-consuming or costly to accomplish than expected; and operating costs and business disruption following the merger, including adverse effects on employee retention and on our business relationships with third parties, including manufacturers of radios, retailers, automakers and programming providers. Additional factors that could cause SIRIUS’ and XM’s results to differ materially from those described in the forward-looking statements can be found in SIRIUS’ and XM’s Annual Reports on Form 10-K for the year ended December 31, 2006, which are filed with the Securities and Exchange Commission (the “SEC”) and available at the SEC’s Internet site (http://www.sec.gov). The information set forth herein speaks only as of the date hereof, and SIRIUS and XM disclaim any intention or obligation to update any forward looking statements as a result of developments occurring after the date of this communication.

Important Additional Information Will be Filed with the SEC

This communication is being made in respect of the proposed business combination involving SIRIUS and XM. In connection with the proposed transaction, SIRIUS plans to file with the SEC a Registration Statement on Form S-4 containing a Joint Proxy Statement/Prospectus and each of SIRIUS and XM plans to file with the SEC other documents regarding the proposed transaction. The definitive Joint Proxy Statement/Prospectus will be mailed to stockholders of SIRIUS and XM. INVESTORS AND SECURITY HOLDERS OF SIRIUS AND XM ARE URGED TO READ THE JOINT PROXY STATEMENT/PROSPECTUS AND OTHER DOCUMENTS FILED WITH THE SEC

CAREFULLY IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION.

Investors and security holders will be able to obtain free copies of the Registration Statement and the Joint Proxy Statement/Prospectus (when available) and other documents filed with the SEC by SIRIUS and XM through the web site maintained by the SEC at www.sec.gov. Free copies of the Registration Statement and the Joint Proxy Statement/Prospectus (when available) and other documents filed with the SEC can also be obtained by directing a request to Sirius Satellite Radio Inc., 1221 Avenue of the Americas, 36^th Floor, New York, NY 10020, Attention: Investor Relations or by directing a request to XM Satellite Radio Holdings Inc., 1500 Eckington Place, N.E. Washington, DC 20002, Attention: Investor Relations.

SIRIUS, XM and their respective directors and executive officers and other persons may be deemed to be participants in the solicitation of proxies in respect of the proposed transaction. Information regarding SIRIUS’ directors and executive officers is available in its Annual Report on Form 10-K for the year ended December 31, 2006, which was filed with the SEC on March 1, 2007, and its proxy statement for its 2006 annual meeting of stockholders, which was filed with the SEC on April 21, 2006, and information regarding XM’s directors and executive officers is available in XM’s Annual Report on Form 10-K, for the year ended December 31, 2006, which was filed with the SEC on March 1, 2007 and its proxy statement for its 2007 annual meeting of stockholders, which was filed with the SEC on April 17, 2007. Other information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the Joint Proxy Statement/Prospectus and other relevant materials to be filed with the SEC when they become available.

***

The following is a press release issued on April 17, 2007.

For Immediate Release

SIRIUS SATELLITE RADIO CEO MEL KARMAZIN
REITERATES BENEFITS OF SIRIUS-XM MERGER

Washington, DC and New York, NY — April 17, 2007 — SIRIUS Satellite Radio (Nasdaq: SIRI) and XM Satellite Radio (Nasdaq: XMSR) announced that SIRIUS Chief Executive Officer, Mel Karmazin, testified today in a hearing before the Senate Committee on Commerce, Science & Transportation regarding the SIRIUS-XM merger. Mr. Karmazin’s testimony highlighted the significant benefits for consumers resulting from the proposed merger and the extensive competition that satellite radio faces from a wide range of players in the audio entertainment market. In his testimony, Mr. Karmazin stated:

The Combined Company Will Offer Consumers More Choice At Lower Prices

The key to getting more subscribers will not be to widen the price gap between free and what satellite radio charges. Instead, it will be to offer consumers a better value.

The merger will allow us to lower prices. Consumers who want fewer channels than currently offered will be able to select one or more packages of channels for less than $12.95 per month.

Importantly, significant portions of the savings achieved through the merger will be shared with customers immediately and in the long-term through lower prices and improved service offerings.

Satellite Radio is a Small Part of a Highly Competitive and Ever-Expanding Market for Audio Entertainment

The audio entertainment market today is vibrant, competitive, and innovative, and every indication is that it will be even more so in the future. We believe that the combination of SIRIUS and XM will be good for consumers as it will intensify this competition, expand the choices for consumers, and reduce prices.

The market for audio entertainment in the United States is robustly competitive and rapidly evolving. SIRIUS and XM must compete directly and intensely with a host of other audio providers for consumer attention.

The Merger Will Help Accelerate Deployment of Advanced Technology

The combined company will be able to offer consumers access to advanced technology sooner than would otherwise occur. In particular, the marriage of the companies’ two

engineering organizations will ensure better results from each dollar invested in research and development.

While no radio will become obsolete as a result of this transaction, we fully expect the merger to stimulate the development of new interoperable, highly portable, low-cost, and user-friendly devices.

# # #

About SIRIUS

SIRIUS, “The Best Radio on Radio,” delivers more than 130 channels of the best programming in all of radio. SIRIUS is the original and only home of 100% commercial free music channels in satellite radio, offering 69 music channels. SIRIUS also delivers 65 channels of sports, news, talk, entertainment, traffic, weather and data. SIRIUS is the Official Satellite Radio Partner of the NFL, NASCAR, NBA and NHL, and broadcasts live play-by-play games of the NFL, NBA and NHL, as well as live NASCAR races. All SIRIUS programming is available for a monthly subscription fee of only $12.95.

SIRIUS Internet Radio (SIR) is a CD-quality, Internet-only version of the SIRIUS radio service, without the use of a radio, for the monthly subscription fee of $12.95. SIR delivers more than 75 channels of talk, entertainment, sports, and 100% commercial free music.

SIRIUS products for the car, truck, home, RV and boat are available in more than 25,000 retail locations, including Best Buy, Circuit City, Crutchfield, Costco, Target, Wal-Mart, Sam’s Club, RadioShack and at shop.sirius.com.

SIRIUS radios are offered in vehicles from Audi, Bentley, BMW, Chrysler, Dodge, Ford, Infiniti, Jaguar, Jeep^®, Land Rover, Lexus, Lincoln, Mercury, Maybach, Mazda, Mercedes-Benz, MINI, Mitsubishi, Nissan, Rolls Royce, Scion, Toyota, Volkswagen, and Volvo. Hertz also offers SIRIUS in its rental cars at major locations around the country.

Click on www.sirius.com to listen to SIRIUS live, or to purchase a SIRIUS radio and subscription.

About XM

XM (Nasdaq: XMSR — News) is America’s number one satellite radio company with more than 7.6 million subscribers. Broadcasting live daily from studios in Washington, DC, New York City, Chicago, the Country Music Hall of Fame in Nashville, Toronto and Montreal, XM’s 2007 lineup includes more than 170 digital channels of choice from coast to coast: commercial-free music, premier sports, news, talk radio, comedy, children’s and entertainment programming; and the most advanced traffic and weather information.

XM, the leader in satellite-delivered entertainment and data services for the automobile market through partnerships with General Motors, Honda, Hyundai, Nissan, Porsche, Subaru, Suzuki and Toyota is available in 140 different vehicle models for 2007. XM’s industry-leading products are available at consumer electronics retailers nationwide. For more information about XM hardware, programming and partnerships, please visit http://www.xmradio.com.

***

This press release contains “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements include, but are not limited to, statements about the benefits of the business combination transaction involving SIRIUS Satellite Radio Inc. and XM Satellite Radio Holdings Inc., including potential synergies and cost savings and the timing thereof, future financial and operating results, the combined company’s plans, objectives, expectations and intentions with respect to future operations, products and services; and other statements identified by words such as “anticipate,” “believe,” “plan,” “estimate,”

“expect,” “intend,” “will,” “should,” “may,” or words of similar meaning. Such forward-looking statements are based upon our current beliefs and expectations and are inherently subject to significant business, economic and competitive uncertainties and contingencies, many of which are difficult to predict and generally beyond our control. Actual results may differ materially from the results anticipated in these forward-looking statements.

The following factors, among others, could cause actual results to differ materially from the anticipated results or other expectations expressed in the forward-looking statement: general business and economic conditions; the performance of financial markets and interest rates; the ability to obtain governmental approvals of the transaction on a timely basis; the failure of SIRIUS and XM shareholders to approve the transaction; the failure to realize synergies and cost-savings from the transaction or delay in realization thereof; the businesses of SIRIUS and XM may not be combined successfully, or such combination may take longer, be more difficult, time-consuming or costly to accomplish than expected; and operating costs and business disruption following the merger, including adverse effects on employee retention and on our business relationships with third parties, including manufacturers of radios, retailers, automakers and programming providers. Additional factors that could cause our results to differ materially from those described in the forward-looking statements can be found in our Annual Report on Form 10-K for the year ended December 31, 2006 which is filed with the Securities and Exchange Commission (the “SEC”) and available at the SEC’s Internet site (http://www.sec.gov). The information set forth herein speaks only as of the date hereof, and we disclaim any intention or obligation to update any forward looking statements as a result of developments occurring after the date of this press release.

Important Additional Information Will be Filed with the SEC

This communication is being made in respect of the proposed business combination involving SIRIUS and XM. In connection with the proposed transaction, SIRIUS plans to file with the SEC a Registration Statement on Form S-4 containing a Joint Proxy Statement/Prospectus and each of SIRIUS and XM plan to file with the SEC other documents regarding the proposed transaction. The definitive Joint Proxy Statement/Prospectus will be mailed to stockholders of SIRIUS and XM. INVESTORS AND SECURITY HOLDERS OF SIRIUS AND XM ARE URGED TO READ THE JOINT PROXY STATEMENT/PROSPECTUS AND OTHER DOCUMENTS FILED WITH THE SEC CAREFULLY IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION.

Investors and security holders will be able to obtain free copies of the Registration Statement and the Joint Proxy Statement/Prospectus (when available) and other documents filed with the SEC by SIRIUS and XM through the web site maintained by the SEC at www.sec.gov. Free copies of the Registration Statement and the Joint Proxy Statement/Prospectus (when available) and other documents filed with the SEC can also be obtained by directing a request to SIRIUS Satellite Radio Inc., 1221 Avenue of the Americas, New York, NY 10020, Attention: Investor Relations.

SIRIUS, XM and their respective directors and executive officers and other persons may be deemed to be participants in the solicitation of proxies in respect of the proposed transaction. Information regarding SIRIUS’ directors and executive officers is available in its Annual Report on Form 10-K for the year ended December 31, 2006, which was filed with the SEC on March 1, 2007, and its proxy statement for its 2006 annual meeting of stockholders, which was filed with the SEC on April 21, 2006, and information regarding XM’s directors and executive officers is available in XM’s Annual Report on Form 10-K, for the year ended December 31, 2006, which was filed with the SEC on March 1, 2007 and its proxy statement for its 2006 annual meeting of shareholders, which was filed with the SEC on April 25, 2006. Other information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the Joint Proxy Statement/Prospectus and other relevant materials to be filed with the SEC when they become available.

***