"Our global active install base of iPhones continues to grow and has reached an all-time high at the end of December," Maestri said. "We are disclosing that number now for the first time as it has surpassed 900 million devices, up year-over-year in each of our five geographic segments and growing almost 75 million in the last 12 months."

Apple CFO Luca Maestri said during Apple's fiscal Q1 earnings call Tuesday evening that Apple has 900 million iPhones in active usage, and the company will occasionally update this installed base number. This replaces quarterly unit sales, which Apple stopped reporting this quarter .

In total, there are more than 1.4 billion active Apple devices, which includes iPhones and all other Apple products.

The change is another example of how the company is trying to shift investors' focus to its fastest growing business segment, services, as device sales slow down.

Services revenue rose 19.1 percent from a year ago in the December quarter, and Maestri added that revenue from Apple's subscription services, like iCloud and Apple Music, is "growing above Apple's services average."

In contrast, iPhone revenue dropped 15 percent.

By talking about installed base, Apple reminds investors that it has nearly 1 billion iPhones in the wild that generate recurring revenue, whether from subscription services or from transactions, such as purchases in the App Store or via Apple Pay. With the smartphone market growing saturated and stiff competition from lower-priced models, particularly in China, it may be easier for Apple to grow by earning a little more money from each of those users every quarter than by increasing the number of or average price of iPhones.