Napster

( NAPS) launched its planned mobile music service in Japan on Monday.

The service runs on

NTT DoCoMo's

(DCM)

iMode mobile internet platform, which is used by over 40 million of DoCoMo's 52 million subscribers in Japan.

For about $3 a month, DoCoMo customers can access full-length songs and ringtones wirelessly. Those subscribers will also receive 300 credits a month, which can be used to buy individual tracks and ringtones.

Napster shares were off 2 cents to $4.79 in recent trading.