Vodafone launched their sim only deal for Iphones - £25 per month for 900 mins, 3000 texts and 1gb of data download limit. 12 month contract.
Quidco are currently doing £160 for this 12 month sim only deal. works out at £11.66 per month.
Quidco ends the end of march.
Warning - Quidco does not always track - though you do have a 14 day cooling off period.