Apple's iPhone 3G has been an international hit and sold millions of units, but some customers have been experiencing reception issues in areas that previously had good coverage.

While the handset's powerful hardware and 3G capabilities are a major part of its appeal, a pair of wireless carriers recently said these may be causing the reception problems.

For some users in Australia, the iPhone 3G has been suffering from slow Internet speeds and spotty call quality. A spokeswoman from Vodafone, an iPhone carrier, said the problems were device-specific and weren't being caused by the carrier's networks.

"We are aware of the issue on the iPhone 3G and we're working with Apple to provide a solution," the spokeswoman told The Sydney Morning Herald.

An unnamed source also told The Herald that Apple didn't give the carriers enough time to thoroughly test the iPhone 3G on its networks prior to launch. Representatives from Apple did not respond to press inquiries.

In a company blog posting, T-Mobile's Netherlands division said Tuesday the problem was probably hardware-specific. But the company backed off that claim Wednesday and simply acknowledged that the user experience for iPhone 3G customers "is not enough."

Complaints have cropped up from users across the globe regarding poor connections and spotty 3G coverage, indicating that the problem may not lie with a specific carrier or network.

"I live in downtown Los Angeles, where 3G coverage is a given, and not only is the 3G wonky and unreliable, but oftentimes I'm struggling to even get decent Edge support!" read one message on Apple's discussion forum. "Edge is absolutely worse on my new 3G than it ever was on my first generation iPhone. Adding insult to injury, I drop multiple calls every day, something that rarely happened before my 'upgrade.' "

In a report Tuesday, Nomura analyst Richard Windsor said an "immature" chipset from Infineon could be the cause of the reception issue. Infineon did not comment by press time.