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iPhone users have been complaining since launch of dropped calls when the phone switches between 3G and Edge areas, and a lack of 3G connectivity even in 3G areas.

"We believe that these issues are typical of an immature chipset and radio protocol stack where we are almost certain that Infineon is the 3G supplier," claims Nomura analyst

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Richard Windsor. "There are too many instances on iPhone blogs and Apple's own website for it to be coincidence. Furthermore, it is not just the US but other countries as well."

A separate BusinessWeek report also cites an unidentified source as saying the problem lies with Infineon technology, which it describes as "fairly new and untested in high volumes outside a lab setting."

BusinessWeek reported that Apple had set up the Infineon chip to demand a more powerful 3G signal than it needed, resulting in a switch back to the slower network if there are too many people in the same area trying to use their iPhone at the same time.

The problem affects 2% to 3% of iPhone traffic, BusinessWeek claims.

Infineon spokesman Guenter Gaugler declined to comment on the iPhone, but notes that the German chipmaker has been supplying 3G chipsets to phone makers such as Samsung Electronics without any problems.