Got myself a sim free Galaxy S5 earlier this month...brand new sealed off Gumtree for a good price.
1 month left on my 24 month Vodafone contract (£36.80 p/m) which I was looking to cancel as I was eyeing up going with the £15 3 Sim offer.
Rang up Vodafone this morning and they offered me for £15.50 Unlimited Texts, Unlimited Calls and 8GB 4G Data, along with either a free subscription to Netflix / Sky Sports / Spotify, as I am already to subscribed to Netflix I get a 6 month credit applied to my account.
Asked if Vodafone could do anything better and they offered me a credit of £15.50, so the total cost per month is £14.21 per month / £170.50 for 12 months / £134.56 (taking Netflix credit into account)
Personally don't think that is a bad deal for a 'tier 1' network operator, admittedly will most likely only apply to customers coming towards the end of their contract.