Not quite a direct deal or available for everyone. Called Carphone Warehouse for an upgrade and was offered 18month sim only cash back £25 a month 200min 400txt and web bolt on and additional 50min off peak min as treat. The cash back is £400 paid in three installments every six months.
Iphone costs £440.40 on pay as you go, to this end as long as your willing to part with the £440.40 upfront over 18months stick your new contract SIM in and it will cost you spread over the 18 months £27.25 for the new Iphone. Poss £5 through quidco if buying online once the phones available, getting mine through Apple Store as they have it in stock.