Its reputation has already been tarnished by iPhone 4 antenna problems, but now Apple faces a new PR nightmare as iPhone 3G owners say their handsets are barely usable after Apple pushed out a software update.

The iOS 4.0 update was recently delivered to iPhone 3G users when they connected the device to their computers. Many users have said their phones now regularly lock up and take an eternity to perform basic tasks such as web browsing.

Anthony Agius, founder of the popular Australian MacTalk community website, described the update as a "disaster" for iPhone 3G owners.

"It's just so slow, apps don't run properly; to launch the SMS app for example might take 30 seconds, Safari chugs ... the OS [operating system] itself will freeze," he said, adding the problems persisted even with the recent minor iOS 4.0.1 update.

"Apple blocked it so you can't go back to version 3, so if you don't like it you're stuck with it. Personally I think they just made a bad choice by releasing iOS 4 for the 3G without checking it properly."