Total shipments of iPhone devices, including updated iPhones which are to be unveiled shortly, are expected to total 45-50 million units in the third quarter of 2015 and hit 70-80 million in the fourth quarter, according to sources from Taiwan's iPhone supply chain.

The estimated iPhone shipments are based on Apple's demand for parts and components for the two quarters, said the sources, adding that shipments of the updated iPhones will start gaining momentum in September.

While demand for the new iPhones is expected to continue into the first quarter of 2016, the sources estimated that the growth momentum for the devices may not be as strong as that for the iPhone 6 and iPhone 6 Plus, commented the sources.

However, production of the updated iPhones at Foxconn Electronics and Pegatron is expected to proceed smoothly as there are no shortfalls of force touch panels, camera modules, processors and memory devices, revealed the sources.