Well, O2 promised an upgrade offer earlier this week for the new iPhone 4 and now the company has delivered it - but it will mean paying out for your old contract.The deal is pretty straightforward. The early upgrade offer, which is valid from 24th June to 24th July, will enable you to pay a 'reduced one-off charge' to get your hands on the latest Apple smartphone, that charge varying depending on how long your 'minimum term' has to go.It's easy enough to work out though. Instead of paying off your remaining contract in full, O2 will charge £20 for each full month left on your contract. So if you've got 6 months still to go, pay the company £120 upfront and you can sign up for a new iPhone. If you don't know your renewal date, from mid-day today you can text DATE to 21302 to get it sent to you.Good deal? Depends how desperate you are to get your hands on the new model. iPhone 3GS users will get an OS update to 4.0 anyway for free, so if you can hold out, it might save you a few quid. If not, well the offer's there. At least it is for the first month of sales.