By Kasper Jade

Published: 02:30 PM EST

With a flick of a switch Apple Computer could debut a subscription-based sales model for its iTunes music download service, says one analyst who believes Yahoo's new music service clearly poses a problem for Real Networks and Napster, but questions whether it will have a significant impact on Apple.

In a research note released to clients on Thursday, Merrill Lynch analyst Steve Milunovich said the current weakness in Apple's stock represents a buying opportunity. The analyst acknowledges that the news flow over the past week has opposed Apple, but said his firm maintains a long-term bullish outlook for the company.

Earlier this week, The Wall Street Journal's Walt Mossberg endorsed Yahoo! Music as the "best subscription service." Meanwhile, Microsoft Chairman Bill Gates followed with a few jabs of his own -- proclaiming that mobile phones should replace the iPod as the primary device for listening to music, and hinting that Apple shouldn't get too comfortable with its current position.

In regards to the pressure from Yahoo, Apple could "flick the switch on a subscription model," Milunovich believes. He says Apple could debut an iTunes subscription model later this year if it experiences any share loss as a result of Yahoo! Music and similar subscription services. To date, subscription services account for a mere 15% of the digital music download market while iTunes boasts an over 70% share.

Additionally, Milunovich noted that number of song downloads from Apple's iTunes are actually accelerating. He estimates that the average iPod user has only paid for and downloaded about 20 songs. At the same time, Yahoo's music service remains unproven, and could present issues of its own. Such problematic issues could include Yahoo's: use of advertisements, potential to raises fees, and reliance on the Microsoft WMA format, which could disinterest some consumers.

As for the comments from Gates, Milunovich argues that Apple isn't standing still and is working to protect its iPod profits. "Industry observer Robert Cringely examined the new Tiger OS and found unused icons and support of the H.264 codec that hint at video capability on the iPod and an iTunes video store," the analyst said. "Cringely also believes Tiger may have support for competing music formats, indicating that if iPod margins get squeezed Apple might license its software and switch to software-driven profits. That’s more of a stretch though Apple does appear to have learned from past mistakes."

In the eyes of Merrill Lynch, the Apple story is about more than iPods. "Although we think the iPod franchise is safe for at least the next year, the driver of the stock increasingly will be Mac sales," Milunovich wrote on behalf of the firm. "Management sees more evidence of the halo effect. We model a conservative 15-20% sustainable growth rate for Mac revenue. "

Merrill Lynch reiterates a "Buy" rating on Apple with price objective of $51 a share.