The mobile networking is offering the 16GB version of Apple's latest smartphone for £495, or the 32GB versions for £595.
O2 is also offering PAYG users 300 free UK texts and a 500MB data allowance when they top up £10 per month.
Apple's latest smartphone was unveiled by Steve Jobs at the company's Worldwide Developers Conference (WWDC) in June.
The new handset, which features an all-new design, has "well over 100 new features" including an HD screen, video calling, a gyroscope, a new iMovie app and countless other upgrades.
Fore more information or to purchase the iPhone 4, visit O2's dedicated web page.
If you want a pay monthly contract for the iPhone 4, you can compare the best iPhone 4 deals here.