Apple (Nasdaq: AAPL) has a tradition of announcing iPhones in June and releasing them shortly thereafter. This year, there are rumors the upcoming iPhone 5 won't launch until the fall. The iPhone accounts for about 39% of Apple's revenues, so a delay should put earnings forecasts at risk.

What's more, a lot of AT&T (NYSE: T) iPhone contracts start coming up for renewal in June and early July. A fall iPhone 5 launch would open a window for smartphone competitors to poach iPhone owners. That could be good for smartphone competitors Research In Motion (Nasdaq: RIMM), Motorola Mobility (NYSE: MMI), Nokia (NYSE: NOK), Hewlett-Packard (NYSE: HPQ), and Samsung.

Two pieces of news are driving the rumor. According to a report out of Asia, Apple suppliers have not yet received parts orders, and the iPhone 5 won't contribute to fiscal 2011 revenue.  In addition, invitations to Apple's Worldwide Developer Conference in June went out on March 28th, indicating it will be "a preview of the future of iOS and Mac OS X."

Preview? The future of? Usually the new iOS is launched with the new iPhone at that conference. But there was no mention of the iPhone in the invitation.

Apple may intentionally delay the iPhone 5 to wait for second-generation Qualcomm (Nasdaq: QCOM) LTE chipsets. When Apple introduced the Verizon version of the iPhone 4, which began shipping in February, management said the first generation LTE chipsets would "force some design compromises" that the company wouldn't make. The aforementioned Asian report noted Apple is focused on adding Verizon customers.

Then again, maybe Apple is just trying to avoid another AntennaGate type of episode.

BMO Capital said it expects the iPhone 5 introduction "in the September quarter," which starts in late June. Jefferies & Company is taking the rumors more seriously, cutting estimates for Apple's fiscal year 2011, which ends in September. With three quarters left to report in the year, Jefferies cut its revenue forecast by 4% to $103 billion and its EPS forecast by 5% to $23.03.

Foolish takeaway
Apple shareholders may have a rotten summer. An iPhone 5 delay could cause earnings and revenue to fall short of current expectations. In addition, Pacific Crest recently expressed caution about June quarter forecasts due to supply disruptions in Japan. If true, that could bruise Apple's earnings call on April 20th.

To stay updated on all things Apple, add the company and its competitors to our free My Watchlist service.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.