Napster (NSDQ: NAPS), very slowly building up its mobile operator clients, has signed on UK and European operator O2, to launch a music service on the operator’s platform. Five million songs will be available, from major labels and 168 indies. O2 subscribers will be charged 99 pence for downloading single tracks, or GBP4 for five songs..data usage costs included in the price. It will be available on 30 different handsets.

O2 has a UK exclusive for Apple (NSDQ: AAPL) iPhone, but the Napster service won’t be available on the iPhone.