JMP Securities is now covering digital music stocks and offered praise for Apple but caution for Napster and RealNetworks, reports the AP.

Not that digital music can really be called a killer app, but JMP Securities' Ingrid Ebeling said, "We believe digital music will be the killer app in 2006 and 2007."

Later she wrote about the growth of subscription services. "The market for subscription services will likely accelerate at a slower pace than the pay-per download market as consumers will likely chose the own rather than rent model, but over time we believe subscription customers will grow as they migrate to the portable subscription services."

She was cautious about Napster, which she believes will break even at two million subscribers (way up from the current 550,000), and RealNetworks, which she thinks "won't attain operating leverage until 2007, and even then the operating leverage is not expected to be significant."