Howard Stern, King of all Media has left terrestrial radio for satellite. I will miss Howard in the mornings. I used to listen to him about 3 times a week on the way to work.

Sirius Satellite Radio's $500 million investment to add Howard Stern to its programming starting in January has already paid big dividends -- even for its rival, XM Satellite Radio.

In the year since the Stern deal was announced in October 2004, XM, the industry leader, doubled its subscribers to 5 million. Meanwhile, Sirius subscribers increased to 2.2 million by the third quarter of this year, up from about a million at the end of 2004.

The growth has, in part, been attributed to the "Stern effect," according to company officials and analysts. "Howard Stern has raised the awareness of the entire satellite radio category," said Hugh Panero, XM's president.

Sirius expects to have more than 3 million paying customers by the end of this holiday season -- though that is still only about half as many customers as XM expects. Both companies have also recently introduced service in Canada.

Now, the two companies face the tough challenge of differentiating their brands in the minds of consumers, who may well consider them interchangeable.

Each service charges a $12.95 monthly subscription fee (XM raised its price last March from $9.95), and each offers scores of commercial-free music channels.

Check out The Sirius service has 120 channels, and XM has 160.Howard Stern.Com and Howard at his new digs on yahoo. Join the Howard Nationthere.