How to upgrade iphone4 for free?

I don't think you will get an offer from retentions, at least if you want an iphone. Most networks don't seem to offer retention deals on iphone. If you can get an iphone for free on a different network that has signal in your area, then wait to the end of your contract term and ask for your PAC. Then take it to the new network. If the deal you have seen is with O2 then remember that you can't port your number within the same network. So you would need to leave O2 for someone else. if you’re paying the highest monthly charge, you should be able to get the iphone 4 for free, however, they will probably only give you the iphone 4 if you extend your new contract to 24 months, and then only a 16gb phone, if u want a 32gb one, they may put a £100-150 supplement on top