Six million people may have upgraded to the iPhone 3.0 software according to Apple, but it seems the vast majority of them are iPhone owners, rather than iPod touch.

Mobile advertising firm AdMob has been analysing requests from its network of ads from both devices, and says that of those from iPod touches, just 1 per cent are from the 3.0 OS.

It blames the fact that iPod touch owners have to pay for the upgrade. iPhone owners don't, and AdMob's figures suggest 44 per cent of them have upgraded to 3.0.

"Developers looking to sell applications utilizing the 3.0 features can’t be happy with Apple’s decision to charge for the upgrade as it limits their available market size for downloads," says AdMob in its blog post.

We'd love to hear your views if you're an iPod touch owner: have you upgraded, and if not, what's stopping you? Let us know with a comment.