Vodafone sim only deals back with high cash back levels at quidco.
Best is £15/month with £115 quidco working out at just £5.41 per month.
It looks as though this is available on iphone 300mins, 500mb data, unlimited texts
Also £120 cashback on £20 deal = £10 month after cashback. 900 mins, unlimted texts, free 0800 etc, 500mb data (not iphone)
other good deals as well