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.
O2 said that instead of paying off the remaining contract in full, it would let its customers that wanted to take out a new iPhone 4 contract, pay a one-off charge based upon a £20 per month fee for each full month left to run on the contract.
However, none of the UK networks have yet revealed pricing details for the handset.
O2 customer interested in upgrading can visit the network's dedicated upgrade web page and enter their upgrade date to get an estimate as to how much the one-off charge will be.
However, the network did say the scheme could not be used in conjunction with an early upgrade eligibility that might already exist.
O2 customers looking to get their hands on the iPhone 4 might want to consider making use of O2's mobile phone recycling scheme.
Under the scheme, O2 will pay a cash sum into your bank in exchange for your old mobile phone and battery.
Those looking to recycle a 16GB Apple iPhone 3G can get their hands on £173, which O2 customers could use to extract themselves from their current contract and even leave enough left over to pay the expected handset charge.
However, we have noticed the cash sum is decreasing daily, so users will need to recycle their handset quickly.