Napster Inc. said its subscription service will become available to between 5 million and 6 million AT & T; Inc. mobile phone customers next month.

“When AT & T; turns this on, we will have access to 5 million subscribers virtually overnight,” Napster Chief Executive Chris Gorog told Bloomberg News.

AT & T; will inform subscribers about the Napster service in “a couple of weeks,” he said.

The Los Angeles-based online music subscription service is focusing on increasing subscribers through deals with cellular carriers. Besides AT & T; in the United States, it is working with NTT DoCoMo Inc. in Japan.

The service allows subscribers to download five songs a month to their mobile phones and computers for $7.95.

AT & T; first began to offer Napster’s service last year but hasn’t drawn many customers because few mobile phones were capable of interfacing with Napster to download the songs.

“We expect a very significant increase in our Napster Mobile revenue in fiscal year ’09 and this AT & T; relationship will be a significant part of that,” Gorog told Bloomberg.

Napster had 760,000 paid subscribers to its music service at the end of March, up 2.3 percent from December. Napster posted results Wednesday that exceeded Wall Street expectations but guidance fell short of expectations.

Shares in Napster closed down 12 percent Thursday to $1.43.