Apple's active subscriber base has ballooned to more than 500 million.

Although Apple's total subscriber base is just half that of Facebook's, Apple's base - arguably, of course - is more valuable. You see, Apple's half a billion active user base (which means these users have active credit cards on file) exceeds Facebook's active user base of just 200 million.

According to Morgan Stanley, Apple is now second only to Facebook in terms of global user base size. Consequently, Morgan Stanley analyst Katy Huberty has reiterated Apple at Buy and maintains a price target of $540.00.

As of Tuesday afternoon, shares of AAPL are trading just south of $450.

"We see two ways to unlock value [for Apple]," a new report from Morgan Stanley reads. "1) Low-end iPhone and iPad Mini will/is growing the user base, which increases the potential revenue impact of new services. Every $1 billion of new services revenue contributes $8 billion of valuation based on peer valuation. 2) Based on historical behavior and our December 2012 iTV survey, roughly a third to half of Apple users are likely to buy a new product, like iTV or iWatch, which accelerates revenue growth and expands valuation multiples."

Source: Benzinga