A research report from Nomura and an article from BusinessWeek are both suggesting that the iPhone 3G has a chip fault.
In particular, they report that iPhone 3G users are complaining that their internet speeds aren't up to scratch and also that the device will use EDGE technology even when there are 3G connections available.
Some users are also reporting that their calls sometimes get dropped.
BusinessWeek explains in its article that Apple had set-up the Infineon chip to demand a more powerful 3G signal than it needed.
This sometimes results in the phone switching back to the slower network if there are too many people in the same area trying to use their next-gen iPhones at the same time.
The problem affects 2-3% of iPhone traffic, continues BusinessWeek said, citing two "well-placed" sources.
Both BusinessWeek and Nomura also point to problems with the software on the phone's Infineon chip, and the business title adds that Apple is going to release a software update.
Nomura analyst Richard Windsor wrote in a research note: "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".
He added: "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".
Infineon would not comment when contacted by Reuters only to point out that the 3G chipsets are also used on other phones and no problems have been reported.
There was silence from Apple and a spokesman from AT&T dismissed the problems as "not something that's high on our radar screen".