Soldato
With my last 2 upgrades it was always cheaper to stick with sim only and buy the phone on PAYG than it was to either upgrade or new contract.
This is what Im doing now. Giffgaff £12 pm is really good, you can find cheaper for a bit more hassle.
Fed up of paying double for a phone over X months on ****** data contracts, when you can just buy it up front and save in the long run both on overal phone costs and the plan.