Last week, the mobile network AT&T reported subdued demand for upgrades. UBS expects iPhone sales to be around US$45m in the quarter, flat on last year, although it believes revenues and profits will grow, helped by rising iPad sales and demand for more expensive plus-sized iPhones.
Analysts will grill Tim Cook, Apple's chief executive, on whether slow iPhone 8 sales are a sign that shoppers are waiting for the more expensive -iPhone X model or merely buying fewer handsets.
"The weakness in the iPhone 8 probably is more due to strong demand for the X than a disappointing cycle," UBS said. The iPhone X sold out almost immediately when pre-orders opened last week, with some shoppers told to wait several weeks for the phone to be delivered. It suggests that even if there is demand for the high-end device, Apple is struggling to make enough of them.
The iPhone X's new design and complicated 3D sensor system have led to widely-reported production hiccups. It is going on sale two months after its r-elease and supply is unlikely to catch up with demand for months.
Last week Apple was forced to deny a report that it had lowered production standards to boost supply.
Apple's last experiment with releasing two different versions of the iPhone was in 2013, when it unveiled the 5s and a cheaper iPhone 5c.
The latter sold in disappointing quantities and Mr Cook admitted the company had overestimated demand for it.
Apple shares are trading at close to all-time highs, suggesting investors -remain confident about the company's future. Its guidance for the current quarter, typically Apple's most profitable period of the year, will also be -eagerly awaited this week.
For the next quarter, it is expected to report record iPhone sales and profits.
