AT&T’s mobile unit, the largest mobile carrier in the US, will announce plans on Monday for an instant “over-the-air” music download service to be launched next month with Napster, the Los Angeles-based digital music pioneer.

AT&T’s Napster Mobile service will be launched in mid-November and will enable mobile phone subscribers to search, preview, purchase and download music from Napster’s catalogue of more than 4m tracks directly to their handsets.