It’s a debate that’s been raging for a couple of years now. What happens to Apple (NASDAQ:AAPL) once consumers finally lose their manic interest in the iPhone? Fans and followers of AAPL stock, of course, don’t think such a scenario could ever materialize, while veteran investors know that nothing lasts forever.

Like it or not, if you’re in the former camp, there will come a point in the near future when the iPhone is incapable of carrying the weight that it used to. The good news is that the company’s got other things in the works. The bad news is that it’s not going to be potent enough, soon enough, to make up for “peak iPhone.”

Slowing Sales

In its second fiscal quarter ending in March, Apple sold 52.2 million iPhones — more or less in line with analyst expectations of 53 million. It wasn’t a bad showing. That tally was up 3% year-over-year, and considering the November launch of the iPhone X may have been a little too close to the September launch of the iPhone 8, it had to be considered a success.

On balance, however, iPhone sales are at least leveling off, if not at the precipice of falling.

The graphic below plots the same data as above, but on a trailing 12-month basis. That representation overrides any calendar-related, timing-related headwinds that may have worked against the company.

It’s concerning, even though loyal AAPL stock-holders don’t care to admit it.

There is life after the iPhone though, even if not as scintillating as the iPhone has been for over a decade. The question is just how much weight can the iPhone continue to carry?

Alternative Growth Engines

One doesn’t have to look too hard to figure out Apple is stirring a lot of pots now to offset the brewing smartphone headwind.

Chief among those projects is content. Apple earmarked $1 billion for home-grown video content to be made in 2018, and thus far seems to be proceeding full speed ahead. It’s even reportedly tinkering with the production of a feature film.

Another growth engine for Apple, of course, is app sales themselves.

For the better part of the iPhone’s 11-year existence, apps — applications, or the programs that work on your smartphone — were an afterthought, given just enough corporate attention to make the iPhone a must-have. Now those tables are turned. The iPhone is increasingly a means to the end, putting a platform in consumers’ hands that encourages the purchase of apps.

Then there’s the complete rethinking of Apple’s consumer-oriented hardware into something that’s institutional. That is to say, Apple wants companies and government agencies and other institutions to use the iPad and iPhone as a selling or administration tool.

Case in point: Apple and International Business Machines (NYSE:IBM), once at odds with one another in the technology market, have since teamed up to co-create and co-market business-oriented solutions that extract more functionality out of Apple’s hardware. Microsoft (NASDAQ:MSFT) has been a frequent strange bedfellow with Apple too; the two outfits aren’t quite the mortal enemies of each other they’re usually suggested to be.

None of those projects, individually or collectively, are enough to offset the slowdown of the iPhone though.

Reality Check

To be clear, there’s going to be an iPhone of some sort for the foreseeable future. Even if the market is saturated and the distinction between Apple’s phones and those made by rivals like Samsung are narrowing, Apple’s still “the” name in the business. That matters.

Unit sales are slipping, however. And though higher unit prices are offsetting that slow down, that may not be the case forever. At or near $1,000 piece (and more, for top-of-the-line iPhones), more and more consumers are having an “is this really worth it?” moment when they renew their wireless plans.

And the other fronts just aren’t going to help enough.

The entire global film industry is expected to generate $50 billion in revenue in 2020, though bear in mind that’s a fairly fragmented market. The global television industry generates on the order of $270 billion in revenue every year, but that business is even more fragmented than the movie industry is.

Apple’s App Revenue

The business software market, which is a little tougher to define, is worth about $400 billion per year, but that market is littered with even more providers than the television industry is. It would take real so-called “killer app” for Apple to make a meaningful dent in that market, with or without help from IBM or Microsoft. Apple doesn’t appear to be taking that opportunity that seriously. The app market? It will be worth just a little less than $200 billion by 2020. But, that’s a fragmented market too, and Apple only captures a small piece of the price consumers pay for an app at its app store.

Indeed, Apple’s only in a position to capture a small fraction of any of those other markets.

For perspective, last fiscal year, Apple sold $141 billion worth of iPhones. Its “services” revenue, where its video and app sales are logged, only generated about $30 billion worth of revenue last year.

Bottom Line for AAPL Stock

Again, it can’t be stressed enough that iPhone sales aren’t in decline — at least not yet. They may never wane, in fact. It also can’t be stressed enough, however, that the iPhone has been the company’s biggest growth driver, and AAPL stock has largely traded on growth — relative results — rather than reliably-recurring revenue. There’s still plenty of value and cash flow in the cards. But once growth become an even more serious struggle, investors may panic.

And understandably so. There’s life for Apple after iPhone-mania runs its course. That life won’t be nearly as impressive as life has been when the iPhone is firing on all cylinders though.

Just be ready for the impact, though the impact will ease into place rather than hit unexpectedly, and suddenly.

As of this writing, James Brumley did not hold a position in any of the aforementioned securities. You can follow him on Twitter, at @jbrumley.