A decent flip-type phone with 8Gb memory built-in and 3.2 megapixel camera (see sonyericsson.com/cws…980 for more features). Provided you claim according to the T & C, the phone will work out at £100 over the period, i.e. £8.33 per month. Also at the moment Quidco pays £100 for a Vodafone contract phone from Phones4u, so potentially the deal can cost you "0". I suppose there will be costs for posting the 4 redemption certificates, so potential cost of c. £12.
Sony Ericsson W980i on Vodafone 12-month contract @ £25per month - 8 months free line rental (cashback by redemption)