Got an iPhone 3G in the UK? Want to upgrade to a whizzy new iPhone 3GS on 19th June? Well, you can, but there's a cost beyond that of the handset itself.

Specifically, you'll have to pay O2 to end your existing contract before they'll let you sign up to a new one.

O2 revealed the news on its official Twitter feed, telling people that how much they have to pay will depend on how long they have left on their existing contract.

"The early upgrade cost is likely to be monthly cost x months left on your contract, but specifics may vary slightly," they explained.

What that would mean is if you bought an iPhone 3G when it went on sale last July, on a £35 18-month contract, you'll have to pay more than £200 to end it six months early, and that's before the actual cost of buying the new iPhone 3GS.

Which is? In a separate tweet, O2 revealed that the iPhone 3GS 16GB will cost up to £184.98 depending which tariff you sign up to, and the 32GB model will cost up to £274.23. Those highest prices relate to the 18-month £29.38 and £34.26 tariffs, another tweet explained.

In short, the operator is telling its keenest iPhone customers that they'll have to pay more than £385 to get a 16GB iPhone 3GS this month, and more than £475 to get the 32GB model.

Sorry O2, but what's changed since last summer, when first-gen iPhone owners were allowed to switch to the 3G version without paying to cancel their contract?

It's the change in policy we don't understand. And it's not even like iPhone owners are being disloyal - they're signing up to another lengthy contract with O2!

Not cool. Not cool at all. If another UK operator is also selling the 3GS come Christmas, we can see a number of disgruntled early adopters churning from O2 as a result of this.