Ringtones available through Cingular, T-Mobile.

Digital music subscription service Napster has begun offering exclusive mobile content like ringtones, voicetones and wallpaper graphics via a wireless service dubbed Napstertones.

The service is being made available via Napster’s ongoing relationship with mobile media publisher Dwango Wireless and is available to Cingular and T-Mobile subscribers. Additional carriers are expected to support the service this summer.

In conjunction with the service launch, customers will get one free song download from the Napster music catalog if they buy a ringtone via the Napstertones service through June 6. In addition, Napster will introduce a Napstertones prepaid card later this summer, complementing its existing Napster service prepaid card.