Apple discussion boards have reported on-going reception problems with Apple's original and 3G iPhones. The problem leads to dropped calls, poor internet speeds and shortened battery life, say users.
An O2 spokesman said, "We are aware of no particular issues with the iPhone 3G, which was subject to extensive testing before it was launched on the O2 network, and it meets all O2's rigorous network criteria."
Calls to Apple's UK offices went unanswered.
Swedish electronic engineering magazine Ny Teknik reported the problem was related to errors introduced in manufacturing, and suggested a hardware fault.
Other users complained that version 2.0.1 of the iPhone software affects reception, especially of e-mails.
Australian telco Optus is giving credits to 3G iPhone users to compensate for the problems, The Age, an Australian newspaper, reported.
It said Vodafone Australia confirmed the iPhone 3G issues were device-specific, and said it was working with Apple to fix the problem. T-Mobile in the Netherlands said the problem was a "hardware/software issue" specific to the iPhone.