O2 UK has today finally revealed details of how the iPhone 3G will be priced on it’s pay-as-you-go tariffs as well as when the device will be available.

O2 has announced that the unsubsidised iPhone 3G will be available for £350 ($630) and £400 ($720) for the 8GB and 16GB models.

Although once signed up users won’t be forced into a contract, they will be obliged to top-up an amount each month to receive a certain amount of benefits.

Paying between £10 and £14 each month will see users receiving a bonus 500 minutes of call time to any UK home phone or O2 mobile; paying between £15 and £29 adds 1,000 minutes under the same terms, while £30 or more provides unlimited calls.

Unlimited Internet access within the UK, including 3G and O2 Wi-Fi, is free for the first year of service but will cost £10 per month afterwards. Text messages aren’t included and cost 10p each.

The iPhone 3G will be available on pay-as-you-go from O2 starting September 16th.